ThousandsofBolts.com has a huge selection of 108" fabric, usually about $14-15 per yard. I've had very good customer service and fabrics from them.

I have used Thousands of Bolts and they have a huge selection of backing.

I got a set of queen size sheets at dollar discount store for $15.00 and after washing them they do not look bad. Pillow cases came with them also.

I always shop at green fairy.com....great specials and free shipping...Clint, at Green Fairy, is great

Sorry.....make that greenfairyquilt.com

Greenfairyquilts.com

I love Fabric.com, Connecting Threads and Marshalls. Marshalls has the best prices unless you hit a sale elsewhere, and for my purposes have a good selection. Their shipping is reasonable ($5.95 for up to 10 yards). I also use sheets. There is a charity store here that sells sheets for $2.00 - $4.00 depending on size. And many are brand new.

You've gotten quite a few good suggestions, so I would only add MSQS and Thousands of Bolts. Muslin is fine, and so are sheets that can be repurposed.. Sometimes a bedsheet is less expensive

Muslin has been used for years and is great for backing. My DM used bed sheets for her's and they were always hand quilted. I have only used regular quilting fabrics for mine. I think it is up to you what you like the best and what is easy for you to find.

Thank you everyone for all the great suggestions! You have shown me some great places to get fabric and I now have some shopping to do!:o