I agree about using the recycled clothing and yard sale finds. I LOVE that I can look at a quilt I made and see pieces of a garment that my mother-in-law or my children once wore. So, if you are a yard sale addict, like I am, don't just look for the pile of fabric someone is selling, glance at the .25 clothing items.
Using a flat sheet (could also be a yard sale find) for your quilt underside also saves a lot of money.