Visit (Quiltsforsale.ca) and browse the different type/ styles/ sizes to see what they are charging. Many quilts are sold through that site! One of their guidelines is to charge by the square foot- $20 per square foot for fairly basic pieced quilt, up to $30 a square foot for appliqued, or more intricate work. It's just a guideline, place to start.
Another formula is:
Time + materials = Cost
Cost X 2 = wholesale
Wholesale X 2= retail.
There are many formulas used to determine what is fair to the individual seller. Location matters, what might sell for $1500 in one place may sell for $300 in another. Good records are needed and deciding what is reasonable/ fair to you. Don't short change yourself. Remember you might pay a plumber or mechanic $50 an hour - expecting $20 an hour for quilting is Not unreasonable.
I've been charging $20-$25 an hour for 15 years and have never had a problem getting it. Be up front & honest from the beginning