The downside to CHEAP muslin is that it horrible. Loosely woven, nasty to work with, lots of shrinkage. And it is 44" wide.
Now, GOOD muslin, and I use the Kona muslin, is as tightly woven as a good batik, and wonderful to work with. 108" wide and at $12.99 a yard at Joann with a 40% coupon, a good deal.