I have several quilts. I pretty much stick to just a few patterns so I know pretty well how much time it takes to do them.
I find a time when I can pretty much wore a few hours without interruptions.
Each step in making the quilt I write down how long it took.
ironing all the fabric...say 30 min.
Cutting................4 hrs.
Sewing one block or one panel of a strip piece quilt.... so many hrs times how many blocks or panels. etc.
after figuring out how much time to do the quilt, I add on a few hours for extras. $10. hrs is a fair price plus all the materials for the quilt. Haven't figured out how to charge for shopping time :-)