I think here in the Midwest we are fairly on the low side of prices(locally I see that at Happy Crafters and also another quilter in the area that charges wayyy low). That being said, around here, most of us start prices for an open, easy panto at 015cents/ sq inch and heavier pantos at about 2 cents/sq inch. Custom--meaning the borders and center are treated differently and often each block is treated separately (i.e. with a sampler) usually starts at 2 1/2 cents for a very simple design. When you add in lots of ruler work, or more dense quilting, the price climbs up to about 3cents/sq. inch. Heavy quilting or complex designs would be more. And if there are many thread changes, it would also likely result in higher prices. But many of us are realizing that when you charge 2 cents for a 85x90" quilt that takes 30 hours (not counting any design prep work--i.e. doing some drawings, marking the quilt, making stencils, etc)it means you are working for $5/hour. Thus when another quilter decided to start charging by the hour--and one quilt cost $500 (king with custom work at $10/hr) there was lots of talk. A national quilter/teacher announced in a recent class I took that micro quilting is charged at $15 hr. for a 14x14" area (this person timed working on a sample of that size with micro quilting and it's $15 for 1 hr.)and that is on top of the rest of the cost.
So to answer your question--no I don't think it's overcharging.