I bought two sheets yesterday that I intend to use for backing. They are 100% cotton, 200 thread count, 108in x 108in. The cost the equivalent of $17.40 each.
The last time I bought a piece of cotton this big was from Hancocks of Paducah, same thread count, same width, and about $13 PER YARD, then I had to pay shipping on top of that. As far as I am concerned, I will be looking for more of these sheets.