I think anything you use for backing is pricey. You need 6-9 yards of 45" fabric to back something the same size as 3yards of 110" wide muslin. At $5 per yard that is more expensive. It is best, I think to figure that cost in while planning to make your quilt. You can make the top out of scraps, but then how are you going to back it? Yo've got to consider this in the planning. If I find bolts of potential backings on sale, I pick them up. My issue is finding bolts on sale that have enough yardage to be big enough for a quilt back. That Ben Franklin store I found last week had two bolts of fabric at $3.95 per yard of great backing fabrics. I was happy to find it.