In our area they charge by the square inch, depending on the type of quilting. Meandering or simple pantographs are one price, more challenging pantographs are another price, and custom heirloom type is the most expensive. Plus the maker provides the top, backing, batting and pays for the thread.
As a favor to my neighbor I offered to quilt her queen sized quilt and give her batting too for $50. She's a senior citizen and I don't mind doing it for her really cheap. She turned me down!! So, don't feel guilty!!