For most people price is one of the most important parts of any mattress purchase (and one of the biggest limitations) and your budget is certainly part of what will determine the type, quality, and durability of the materials and the types of mattress that will be available to you. While it's certainly not always true in the mainstream industry ... in the smaller part of the industry that sells better quality/value mattresses there is a great deal of truth that "you get what you pay for" so it's important to have reasonable expectations about the type and quality and durability of the mattresses that are generally available in each budget range when you are deciding on your budget for a new mattress. In most cases higher budget ranges will have materials and choices available that have benefits that you can actually "feel" or that will make a difference in the durability and useful life of a mattress. Because of the importance of a good quality mattress ... up to the range where the additional benefits of higher budgets reach a point of diminishing returns (over about $3000 or so), it can be a good idea (within reason) to set a budget range that is the highest you can reasonably and comfortably afford.
Having said that ... there are many mattresses in the industry that use lower quality materials with a "story" attached to them that sell for far more than they should so it's always very important to have a general idea of the type and quality/durability of the materials and mattresses that are available in each budget range. The biggest "tradeoffs" for lower budgets "should be" the the range of good quality and durable materials that are available, the amount of higher quality and more costly materials in the mattress, and the durability and useful life of the materials in your mattress and how long it will maintain its comfort and support before you need to replace it ... not the "marketing story" that goes with the mattress. While the reality is that higher quality and higher performance materials, more specialized materials, and more durable materials will all come with a higher cost ... if you are "armed" with the information on this site about where and how to buy a mattress; your specific needs and preferences and criteria that are important to you; and the differences in the performance, quality, and durability of different materials; you will be much better prepared to differentiate between stories and fact so you can buy a good quality/value mattress that you will sleep well on in any reasonable budget range, even if there are some tradeoffs involved with more limited budgets.
For the sake of simplicity and because it's impossible to categorize every mattress and material in the industry and fit them into specific budget ranges because of all the many variables involved ... I have included more general descriptions for each budget range to provide a better sense of what would be a reasonable expectation for each of them. The prices are based on a queen size purchase which is the most popular choice and for a "mattress only" purchase without a foundation or box spring or any other extras that you may need to complete your sleeping system so that you can make "mattress to mattress" comparisons. Of course a larger size than queen will cost more and a smaller size will cost less and any additional options that you may need (such as a bedframe, foundation, mattress protector, or pillows) will add to the cost of your purchase as well. Because each budget range has such a huge variety of materials and mattresses made by hundreds of manufacturers that would be suitable for different needs, preferences, and individual criteria and because mattresses in any budget range will vary in their designs, materials, quality, and durability... I would use this as a very rough guideline and not take it too literally or use it to evaluate any specific mattress. I would always keep in mind that the price of a mattress is only one part of it's "value" and that the value of a mattress purchase is always relative to how it compares to the other mattresses that you are considering or that are available to you in your area or online (if you are also considering online choices) based on how suitable it is and how well you will sleep on it, how durable it is and how long you will sleep well on it, and on all the other objective, subjective, and intangible parts of your personal value equation that are most important to you.
$400 and less:
This is the budget range where you will generally find "promotional" or what some people call a "throwaway" mattress that would tend to be more suitable for temporary use, for a guest bedroom, or as a lower budget choice for a child. You may find some comfortable and supportive mattresses in this budget range but they generally won't use higher quality materials that will last. You may also find mattresses that use some higher quality and more durable materials but they often won't use "enough" of the higher quality materials to be "comfortable" or "supportive". This is the budget range where you will also find many "cheap Chinese" mattresses that are part of what I call "the race to the bottom" where the quality of the materials are more uncertain and mattresses that have glowing "stories" about how they are "just as good" as mattresses that are many times more costly but of course these will rarely be true. While there will be some rare exceptions ... you won't generally find good quality/value mattresses in this budget range and for normal everyday use you will find many mattresses that will only maintain their comfort and support for a period of months or a very few years. If you are limited to this budget range you will need to do some very careful research to make sure that the materials in your mattress are reasonable quality so you don't end up buying another mattress much too quickly. Most people would be much better off and save money in the longer term by looking for a mattress in a higher budget range than this.
Over $400 - $700:
This is usually the lowest budget range where you will begin to find some better quality and more durable choices and is a more realistic entry level for regular use by adults although there will still be many limitations and tradeoffs in the type of mattresses and materials that will be available to you. In this range you are looking at innerspring mattresses that often use linked coils (Bonnell, Offset, or Continuous coils) or in some cases lower quality or lower performance pocket coils that will have less steel or less coils than higher budget choices. While the innersprings in this category won't be the best quality or best performing innersprings ... they generally won't be the weakest link of a mattress either. I would look for higher quality/density polyfoam comfort layers in this budget range in any innerspring mattress because the comfort layers are generally the weakest link in a mattress in terms of durability. You will also find some mattresses in this budget range that use relatively small amounts of specialty materials such as latex or memory foam or high performance polyfoam comfort layers on top of polyfoam support cores but some of these will include some lower quality materials in the mix as well so you will need to be very careful that there aren't any weak links in a mattress that use specialty materials in this budget range. This is also a good budget range for better quality children's mattresses or guest mattresses. Most of the fabrics or fibers in this budget range will be synthetic.
Over $700 - 1000:
This is the most popular budget range in the industry as a whole and is where you will begin to see some higher quality choices. Because it is the most popular budget range ... it is targeted by many manufacturers and margins may be lower so there can be some good quality/value here. At this price range you will see some better quality memory foam mattresses, some latex hybrid mattresses, and in a few cases you will see some all latex mattresses that are either thinner or that use synthetic latex blends. You will also see some higher quality innerspring constructions with more premium coils, foams, and fibers. Mattresses in this budget range shouldn't have any weak links in the design and should always include materials that would reasonably be expected to last most people 7 - 10 years (or sometimes longer). There are also many mattresses that are sold in this budget range that don't use good quality and durable materials so you should look for some combination of a good quality innerspring or polyfoam support core with good quality memory foam, latex, higher density polyfoam, microcoils or a combination of these materials in the comfort layers. There will still be some compromises necessary in this budget range because it won't include the highest quality mattresses or designs but it would certainly be a reasonable budget range for those who have a more restricted budget and can't afford a more premium mattress. This is also the budget range where you will find most of the "simplified choice" online mattresses.
Over $1000 - $1500:
At this price range you will see latex or latex hybrid mattresses with more complex designs; higher quality innersprings of all types (including pocket coils) with better construction, comfort layers, and more features; memory foam mattresses with higher quality and more complex designs, higher quality/density polyfoam comfort and support layers, some good quality two sided mattresses; and higher quality fabrics and natural fibers in covers and quilting materials. Similar to the previous budget range, there are also some very good quality/value mattresses available in this budget range. While there can still be some compromises needed in this price range ... there will be less of them and there are many people that won't need to go higher than this to find a high quality, comfortable, supportive, and durable mattress if they are looking at retailers and manufacturers that sell better quality/value mattresses.
Over $1500 - $2000:
In this range you will begin to see more very high quality mattresses that use the most costly materials or with special features designed to help with more difficult comfort and support issues. For example you will more commonly see zoned comfort layers and zoned support layers, component mattresses with side by side zoning for two sleepers with different needs and preferences, innersprings with special features or higher quality comfort materials, high quality ticking and quilting (sometimes organic), or thicker mattresses with more layers that are all high quality and durable materials. Specialized fabrics or quilting layers that are more breathable or temperature regulating are also more common here as are construction methods and designs that can be more customized or can improve the overall quality, comfort, and durability of your mattress. This budget range includes some very high quality/value mattresses. As with all the higher budget ranges though, be very careful because there are also many mattresses in this range that should be in a range one or two levels lower but have a "story" attached to them to justify their price or that contain lower quality materials that are a weak link in the design in terms of durability.
Over $2000 - $3000:
Now you are well into more premium budget ranges and for most people it won't be necessary or even be a good idea to go higher than this. There will be very few if any meaningful compromises in this budget range and you can expect the best quality materials in your mattress. Once again though, it is very important here to be educated about different materials as there are also many so called "luxury" mattresses sold in the mainstream industry in this range or even more that use lower quality materials in the mix that would be a weak link in the mattress and belong in lower budget ranges several categories lower (if they are even worth considering at all). Many of these will "look" great (to attract consumers that look more at the outside than the inside of a mattress) or that have an "amazing" story attached to them that can be more misleading than accurate. It is not uncommon to see consumers pay $3000 - $4000 for a mattress in the belief that they are buying something "special" or "more comfortable" or "more durable" when in fact they could have purchased something very similar or even better through a different retailer or manufacturer for much less. Good research about what is in your mattress can really pay off here as many people who buy a mattress in this range will sometimes pay hundreds or even thousands more than they need to because of misinformation they have received about how it is made, the quality or features it has, or because they are "brand shopping" instead of focusing on the quality of the materials in a mattress. When you are in this budget range, you should be able to buy a mattress that only uses the highest quality materials and components in every part and layer of the mattress construction without exception.
Over $3000 - $5000:
The main reason to buy a mattress in this range is because of personal considerations that are more unusual or unique and that often have less to do with value (as most people would define it), comfort, or support than with special features, materials, or designs that may be more important to a minority of consumers with more unique needs or challenges. At this price range you are paying for something which is rarely if ever "necessary" and much of the time you may be overpaying as well. This is the range where "stories" can become very expensive so it is even more important to differentiate marketing information from fact based information. I would take great care to find out the truth behind any story that is used to justify a mattress in this price range since there are so many local, regional, and online manufacturers where you can buy a custom built mattress to your personal specifications, using your choice of materials, ticking, and quilting, for less than this. For those people who are less price sensitive and still consider this price range as reasonable then more exotic or costly materials, designs, and methods of construction, or even extras like "gold impregnated thread" or "essential oils" added to a mattress are options that may be available. Many of these may be of questionable benefit or worse yet have no realistic benefit at all that will actually make a difference in terms of how well you sleep on a mattress or how long you will sleep well so while there may be a few instances where this budget range can be justifiable for some people because of their special needs or preferences ... I would always make sure that there is a compelling reason to spend this much on a mattress that will actually make a difference that you can feel when you sleep on it. This is a budget range where for the most part higher prices are subject to the law of diminishing returns and would only have benefits or be worthwhile considering for a minority of people.
Now you are into the budget range where how you feel "about" a mattress may be more important that how well you sleep "on" a mattress. This is the range of ultra premium mattresses and there is very little that can justify a purchase in this budget range outside of the satisfaction of owning something that is as much a work of art as it is a functional mattress. I would keep in mind that you won't generally sleep any better or have a mattress that will last any longer in this budget range than the budget ranges below it and this is also a budget range that includes some even more costly "stories" for those that don't ask what is inside the mattress they are considering or how it is made. This is also the budget range where you will find mattresses that are hand built and inner tufted using very high quality materials including pocket coils, natural fibers such as horsehair or cashmere, and other higher quality and costly materials and fabrics in the mattress padding and cover. This doesn't mean that some people that can comfortably afford it wouldn't be happy with a purchase in this budget range and there are certainly some very high quality hand built mattresses that can cost as much as $50,000 and take a master craftsman weeks to build a single mattress but the belief that a mattress in this budget range will sleep better or last longer than those that are in lower budget ranges isn't usually accurate and the "real life" benefits of a mattress in this budget range are generally the pride of ownership or satisfaction that can come from owning a mattress that very few people will ever sleep on or can afford.
Hopefully this will help you decide on the budget range that is most suitable for you and help you understand what a "reasonable expectation" looks like relative to different budgets.