You can look on etsy for completed quilts to get a general idea.
Prices can vary widely by geographic area.
To figure it out for yourself, keep careful track of all your time spent on your next quilts. This should give you an idea of how many hours it takes for an average quilt. Multiply the number of hours by what you would be willing to work for. It should be at least minimum wage, even though it's skilled labor. Add to that all your costs. Fabric, thread, batting, patterns, needles, rotary cutter blades etc. Use full retail prices, not what you paid with a coupon or on sale. Many customers will balk at the final price, but don't sell yourself short or work for peanuts.