I've used etsy, ebay, and fabric.com and had good results with what I got. However, if you're ever in Maine, you should checkout a place called Marden's. It's an odd lots type of place, but TONS of quilting fabrics. Not top quality, of course, but more Joann's Fabrics' grade at really cheap prices. I've gotten some great bundles there (enough for a baby quilt) for as little as $5.99
Also from Maine... the Marden's in South Portland is a lifesaver.