it also depends on your location. in the area of a big city, you can charge a lot more because there's more money going around and less competition.
determine how much you want to make each hour. how many hours will it take. if you don't know, overestimate. it still won't be enough hours. then double that, AT LEAST. so it you want $10 an hour for a quilt that takes 10 hours, double $100 and charge AT LEAST $200 (plus all materials). the reason is this: you can do what they can't. that's worth a premium price. your plumber charges, what? $50? to walk into the house. and he charges you for any materials he needs to buy. he's no better at what he does than you are.
if you live in an area where money is tighter, decide on how low you want to go. there is a point at which it doesn't pay any more. below a certain price, people think you should work for free and then get huffy when you want a fair price. they think they can bargain and they don't want to understand that you're already at rock-bottom. if they can't afford to pay you fair price, they have to buy off-the-rack. people can't have everything they want just because they want it.
whatever you decide, good luck. let us know how it works out.