I took a class once in longarming as a business. The instructor said that she charges by the hour, but her customers don't know that. She is good at estimating how long a particular quilt will take, so she estimates the time and gives the customer a range of pricing, say $250-300. When the quilt is done she fixes the price based on the time taken. That way she is paid for her time, and the customer knows the maximum charge up-front.