I worked in a quilt shop for a couple of years. The owner priced the fabric at 65% above cost because that covered some of the costs of shipping she had to pay. Quilt shops are a lot more than just fabric. They offer us classes, their knowledge, new techniques, and friendly service. You don't get all these things at JoAnn's.
I can tell you this - quilt shop owners work their tails off and make a comfortable living but nothing extravagant.