The first place to start is post #1 here which has all the basic information, steps, and guidelines you will need to make the best possible choices (and help you avoid the worst ones)
Price is certainly not an indicator of value (although it certainly is part of it). Any mattress is only as good as the construction and materials inside it so the only way to make a meaningful assessment of a mattress is by knowing the details of the layers inside it. I wouldn’t make an assumption or go by a “feeling” that a mattress is either good or not so good unless I had the specific information I needed. Almost all latex is a relatively high quality material compared to polyfoam no matter what type it is although like any material there are higher and lower quality versions compared to other types of latex.
Same comments would apply here. Once you know the details of every layer in a mattress you are considering then you can make meaningful quality and value comparisons with other mattresses. Without this information you can’t (and you won’t know how good a “deal” it may be).
As you will read in the guidelines I linked … these are among the ones to avoid completely.
The better options and possibilities I’m aware of in your area are listed in post #2 here.