I stop in the local thrift shop from time to time to see if they have any cheap quilts. I found one this week, one of those WalMart specials where 2 pieces of fabric are sandwiched with batting and then a tiny circle is stitched every 3 feet to hold it all together. PERFECT for playing around on my Tin Lizzie.
I also buy cheap sheets, flannel blankets, etc and use those to practice.