This might be out of your comfort zone, but here goes.
There's a company here in California called Your California Fabric connection, 1-800-479-7906, and they sell scrap bags of quilting fabric. It used to be fairly close to me and I was able to go there and hand pick what I want, so I know that the quality is good --it's brands like RJR, Thimbleblerries, etc. The company moved, however, then almost went out of business, and then found new ownership.
They do carry flannels, so it might be an option for you to buy some. The recent postcard I got says 4 lbs for $43 (free shipping) and 9 lbs for $85, but I don't know if that's the price for flannels. You could call and chat with them, if you don't mind buying the fabric sight unseen.
Laurie