It sounds like the quilt top is already made...no? My long armer charges .02 per square inch for quilting and .25 per linear inch for binding. So, for a top that's 100x100, she would get $200 for quilting and an additional $100 for the binding. If you have to make the quilt top too, then I guess you have to figure out a formula. When I make jewelry, it's always at least 3x the supply cost to figure retail. If my supply cost is low, but time investment is high, I have gone as high as 5x supplies.