A simple pricing formula: Hours spent making the quilt x national minimum wage + any expenses (like materials, phone calls, postage, etc.) = most likely a price that your customer would not be willing to pay.
Also remember: Your 1st customer will no doubt be delighted with the quilt and so tell others. They may come to you and expect the same price.
Good luck with that quilt!
I decided a long time ago that it works best for me to have a demanding full-time job that pays all my basic bills, so quilting can remain a relaxing hobby. A lot of what I make is given away. Suits me, and no pressure.
Lorchen