In figuring this charge you would figure the time it takes to do it and the sizze to be done. Since they will supply fabric and you will do the cutting and sewing just figure how much time it takes to do the quilt and charge according to that. If it takes 2 hours start to finish it would be $20 if it took 5 hours that would be $50. I use to do sewing for a living and this is how I set my fees. One basic fee of ??? and per hour sounds fair to me.