Welcome 7Darlings! Flannel is best for rag quilts in my opinion...so soft after washing. Joanns has a nice assortment of print flannels (
http://www.joann.com/fabric/flannel-fabric/) at reasonable prices...BUT if you watch a bit or sign up for their coupon offers, you can pay a lot less (today I could buy one cut of any size at 50% off, for example). And the Snuggle flannel often goes on sale for $2.99/yard. There are other sources as well. Your local quilt shop many carry flannel, but it probably would be a high quality and higher price that in my opinion isn't really needed in a rag quilt.