How much to charge is such an objective thing, unless you're actually quilting as a business. For many of my friends I would make the quilt for free, from my stash, just to have the pleasure of giving them the gift. Or I might ask that they pay for the materials (if I could not make it from my stash) and would donate my labor. First you should decide whether you really want to make this quilt, and whether it's for the pleasure and experience of making it or for the income you might produce. Either way is perfectly acceptable. If it's for the income, then decide how much your time is worth and charge on that basis. I know there are rules about doubling or tripling the cost of the fabric, but I wouldn't use that formula unless you use a set dollar/yard for the materials, for instance $12/yard. (Why should the customer pay less for your time, just because you found the fabrics on sale or used cheaper quality fabrics?)