I have the same question. I've never sold one and a cousin saw one of my almost completed ones and asked if I would sell it to him. I said I would have to think about it. I would have no idea what to charge. I've looked online and the prices are all over the place from a few hundred dollars to thousands.
I have very vague ideas floating around my head of doing quilting when I retire. I'm trying very hard to be able to retire at 55 and if I could earn a little extra it could be more of a possibility.