Most of the time you would get better results buying sale fabrics at a fabric store like JoAnns. Especially if you get coupons of the internet. Another option is buying 100% cotton shirts at the thrift store and cutting them up for piecing. Sheets do not make good backing fabric because of the density of the thread count. When we first got our longarm and were getting instruction on it the instructor suggested we not accept quilt tops from clients who insisted on using sheets for backing. It makes it very difficult to balance the tension on the top and bottom stitches. Just my humble opinion.