Original works of art are always more expensive than "copies" of art. Quilts are no different. The customer is asking for an original work of art. Consider your time, talent and materials needed to complete the quilt. I would definitely cover your material expenses, time and costs for quilting service. Write up a written proposal a nd collect 1/2 of the $$ upfront before you start work on it. Treat this as a business ....it is.
In the kindness of my heart I offered to do something similar for a local church. Suddenly the original 15 blocks increased to 40 blocks!! None were the same size and I had a ton of prep work to do before even starting on the saashing and assembling the "wallhanging" now queen sized quilt!! I recd $60 for my work! NEVER again!!!
Sandy