I've been to three annual quilting retreats with a bunch of fine quilting ladies, many of whom belong to guilds. Their advice is to charge 3x material.
With that being said, however, I did sell a full size quilt for $500. Some ladies said I way undercharged. Others said that seemed fair because I had not hand-quilted it. Also, I sold a twin size for $150. But it all depends on your location and your customers.
If somebody says they can buy a quilt at Wal-Mart for $20, I say I realize that, but do you want something that will still be intact 10 or more years from now? Do you want something that no one else has? Or do you want something made of inferior materials from a factory?