Hi dfoo,
I think if you look through (or call and talk to) many of the choices on the list you will find many that many of them actually do make and sell some better quality/value memory foam mattresses that are in your budget. While your budget is on the low end of a high quality or more complex memory foam mattress even in twin size … you should be able to find one that uses mid range or better materials in twin size in your budget either locally from the LA list (and there are quite a few of these) or through some of the online vendors (some of which are members here) listed in post #12 here or some of the other better quality/value online vendors that meet your criteria.
Phoenix