long-arm quilting prices vary greatly by location- also your skill level- time involved...it always cracks me up when someone says- a simple stitch in the ditch=since stitch in the ditch is one of the most time consuming/difficult quilting patterns...and usually costs alot more than an all over (panto) design.
some quilters charge by the square inch- and that varies from about 1 1/2 cents up to 3 1/2 cents per square inch- some quilters charge by the project- basing their prices on size and time involved---they generally have a base and the price climbs from their depending on the job.
it would be in your best interest to do some research- call around and ask what the going rate is in your area. what may cost $45 in one area could easily cost $200 some where else. if you are going to base your price on the project itself- decide what your time is worth(i charge $20 an hour just for sewing)
good luck