You have a great idea here! Instead of charging by the hour (
) or by the inch (which is a great idea), would it work to charge by the quilt size? King sized quilts = XX dollars, queen sized quilts = XX dollars, wall hangings measuring less than -- inches x --inches = XX dollars and so on. For odd sized quilts I would measure it and charge the price closest to the size. (Hope this is clear).
Good luck with your endeavor! There are lots of us (me included) out there who don't like to do bindings!