As a professional longarmer, perhaps explaining how I do things will help. Pricing will vary depending on the size of quilt, type of quilting, and where you are located.
The type of quilting can range from a simple edge-to-edge design (also called allover, overall or pantograph) where the same pattern is used across the entire quilt, disregarding the piecing such as blocks, borders sashing, etc. This will be the least expensive - I charge .015 (a penny-and-a-half) per square inch (psi). But I do have a minimum charge of $35.
Custom quilting would encompass setting a different design into each block, border, sashing, etc. For this I charge between .025 and .035 psi.
Heirloom custom includes extensive ruler work such as stitch-in-the-ditch (SID) or crosshatching, tiny background fills, custom motif, etc. This can run as high as .06 psi.
I think I'm considered fairly high for my rural area, but I think I'd be on the low side for a more urban setting. So it all depends on the area you're in.