I think that there was a Fred Meyer in Idaho that used to sell flat sheets. On sale I think it was about $9 for a twin size. I bought a few for quilt backing and they are holding up fine. I even made a couple of skirts for myself out of them, lol!
Quilting is only as expensive as one lets it be. I don't need the latest lines of fabric or new stuff for every quilt. I buy my batting in bulk and so far have found that Wal-Mart online has better buys than Joanns.com.