There is not a set rate, I guess. Depends on what you want. I just do freehand quilting and I charge a penny a square inch plus three dollars for thread and needle and that's it.
I use polycore thread by Efried, it has many colors, and it is a very strong thread. I shy away from pure cotten thread as they will rot over time. I don't do tight meandering. My quilting is like scrollwork that blends into your quilt.
I feel that my price is very reasonable. A 40x48 quilt would cost 22.20 local. My price never changes, unless there is shipping and that is added.
I wanted to be reasonable as I was appalled at the prices I was getting in my area when I needed to get some quilts quilted. I just kept them until I got my own machine.