My thought was, Are you doing this for your MIL or for yourself? Is she paying you to attract quilters or for the privilege of having the quilt displayed in the shop, or will there be a buyer who pays you directly? If it's the former, you can go low. Otherwise, I've turned down offers to make a quilt for pay because there's no way you earn what it's worth. Yours is especially beautiful and intricate and took lots of hours over and above cost of materials.