It depends on the amount and type of quilting - and a few other factors can affect the cost too (the geographic area, the skill of the quilter, additional charges for thread, batting, etc.).
A simple overall meander can start as low as $.01 per square inch, but heirloom quilting can go much higher. Recently I learned that one quilter started her heirloom quilting at $.06 per square inch; another charges $.07 per square inch.
So let's say you had a quilt that was 90"x100" (9000 square inches). The price could range from as low as $90 for a meander up to $630 or more for heirloom quilting.