When I say $9 plus a yard... I like to shop local, because without my local quilt shop I would be lost.
When you make a special quilt, you want the back to be as nice as the top, so I often try to find same fabric family.
If you can shop for sales for backing that is what I prefer.
Our local shops have 20% off if you finish the bolt, so sometimes I get a double % off if it is on sale. Up to 50% off at times.