If you use inexpensive fabric just be careful it will wash well. My saddest tale is that I completed a quilt and only later wondered about the quality of the muslin I'd used. (It's a 30's quilt with muslin serving as the alternate block.) The muslin was just some muslin I had on hand.
So I finally dug up what was left of the muslin I used, cut a 5" square and tossed it in the washing machine (warm water). When it came out of the dryer it was at least a full inch smaller and was horribly wrinkled and felt like cardboard. Since then I have been "unsewing" the whole quilt and replacing the bad muslin with good muslin. So do what you want -- but BE CAREFUL.