I am a Longarm quilter in Iowa. I charge by the square inch...1 3/4 cents (.0175) for e2e... .02 cents for semi-custom... and .03 cents for custom. Customer supplies backing (7inches wider then quilt top and 7 inches longer then quilt top...this allows for loading onto the machine). I also sell 80/20 cotton batting and polyester batting and offer binding service.
So, the quilting on a 60 x 60 quilt top would cost $63.00 (minus taxes and/or other services).