Muslin comes in several price points. choose the one that is more - $1 a yard with a 40% coupon is only 60 cents more a yard. There is a big difference.
The things I have the most trouble with at JoAnn's are the 100% cotton solids. They just can't get them right and they are more than my LQS. Symphony has poly and I rarely mix cotton and cotton/poly in a quilt.
Also not impressed with only Keepsake Cottons on sale, but they're not isolated. Makes finding the sale things interesting.