Walmart has cheaper cotton sheets that work just fine for both machine and hand quilting. I don't use "used" sheets for quilt backs that will be used a lot, but they work fine for wall hangings, table runners, table toppers, etc that will be used seasonally or not washed all the time. If they don't have the color you want dye them in your washer and rinse them multiple times so they won't bleed on other fabrics and off you go! Flannel sheets work well too but are harder to find in single packs.