Where can one buy cheap mattress?

I would go to a discount store. Don't get one at a flea market because that is one way you can bring bed bugs home. Bed bugs are every where these days and you need to be careful. Dateline had a show on this and they went to a reseller of mattresses to see if there were any bed bugs. Even though the mattresses had been "cleaned" they still had bed bugs. Once you get them they are hard to get rid of.