Try Sams Club or Costco. You don't have to buy a set there. Or try your local furniture store and see if they will give you a great price on 8 twins. I can't believe they wouldn't.

Think about air mattresses. They are pretty comfortable and have a sort of sueded surface that will help keep the sheets on the beds. You'll never have to bother with any box springs either. That is a big waste of money and space.

Wouldn't Ikea have mattresses to fit the beds? Or are you looking for something cheaper than Ikea?

How thin a mattress are you looking for? Thinner than a standard twin?

Take a look at Golden mattress company; they are one of the brands we carry and has a very good value. You can get a good twin mattress for about $95 each and would be getting a much better mattress than if you saved $10 or $20 on each mattress. If you are in NC I would be glad to help you out; however outside of NC would kill your deal with the shipping fees.

you can go to a foam store--look one up in your area--they can cut the size you need--think if you needed foam for a window seat--same idea--could even be a memory foam type.