One way to figure cost is to figure the cost of materials--fabric, batting, and backing--then at least double it for your labor. Maybe even triple it. A Dresden block is very labor intensive, so I would charge more. Most people don't realize how much it costs to make a quilt. If they agree with your price, I would get at least half up front. It's very difficult to make any money for a quilt because most people don't want to pay what your labor is worth. Good luck.
Sue