In my neck of the woods it is .015 to .02 per sqaure inch for basic quilting , Custom is a whole different subject can go as high as .10 per square inch.
It depends on if you are supplying the batting , backing , thread and if you want them to do the binding. In my area these are all above the basic costs.
There are plenty of longarm pros on this board who would be happy to provide a quote. Special section in the classified just for such services.