It is a hard question...a lot would depend on the kind of design/pattern you are making. $10.00 per hour minimum plus the materials and if you are having someone else do the quilting, the price of that in addition. I would definitely have the customer buy the materials up front.
I am making a quilt for someone, because he has done my taxes for the last several years at no cost, and I want to do something in return. He said he is probably getting the better deal. He may be right. I will be getting together with his wife to decide on a pattern. I plan on bringing an assortment of patterns that are within the realm of what I am willing to do, nothing too difficult, but nothing too basic either. Then we will go shopping for fabric, and depending on how much that costs, they may help cover the cost of that. We also need to decide on a size, and as long as it is a size I can machine quilt, I will do it as part of the deal, but if it gets too big, and needs to be sent out to be quilted, again, they will pay for that.
I want to do it, so that makes it ok, as I feel very fortunate to have had the help with the taxes.