i think you should have discussed a price before you agreed to make it- it seldom works well to (spring) a price on someone after the fact...if you are going to make quilts for people to purchase the price should be discussed & agreed upon before ever starting the project.
figure out how much time you have into it then decide how much your time is worth...then adjust that to what you think is fair to both of you- i charge $20 an hour for sewing...i also have quilting fees- if i am making a quilt for someone who has supplied the materials (very seldom) we decide if it will be charged by the hour or by the project- pricing is discussed, agreed on and a deposit is paid with the balance due upon completion.