I buy a lot on eBay and from other online sellers - mostly www.fabric.com and www.connectingthreads.com
Fabric.com has great sales and they send you coupons after your order - 15, 20 or 30% off your entire next order. Connecting Threads has great sales and their fabric is gorgeous. Both of them have free shipping if your order is over a certain amount - $35 for fabric.com and $50 at Connecting Threads.