I once read that after 10 years the weight of a mattress nearly doubles in weight from all the dead skin and sweat. That being said, I still paid quite a bit for my bed (around $1200 for a queen) because a good night sleep makes a huge difference during the day. If I'm tossing and turning all night, I'm miserable the next day (and the fiancee is even worse!), so after ten years it's about $120/year or less than $0.33/day (not accounting for inflation), which seems pretty cheap.