My wife and I went out on Boxing day like 5 years ago. We went to the Sears Furniture and Mattress store and did not intend to buy a mattress, we had just gone to look.
We walked in the store and were given a 25% off everything coupon and walked over to the matresses. We saw a $3500 matress and then saw that it was 50% off. We tried it out and really liked it, so in the end we got the $3500 mattress for around $1300, and it is just as new and comfy as the day we bought it.
Price definintely has to do with Quality in regards to a new mattress. But as one poster said above, do not pay anything higher than 50% of the sticker value, they are always going on sale, all you have to do is wait.
We had purchased a $500 one a year before that and within a year we were looking for a new mattress as we were both laying on the boxsprings basically.