These links may be helpful in establishing what you charge as well as to show the customer what others charge. I would think $500 is way too little for this quilt and would honestly charge more. The problem is you didn't discuss price/budget with the buyer and this could lead to some sticker shock. To justify the higher price: It is very complex with lots of different sizes, has an elaborate piano key border and you incorporated the dress in the middle of it.
https://www.toocooltshirtquilts.com/pricing
https://www.tshirtquilts.com/shop
https://www.campusquilt.com/order/index.html