This has often occurred to me (and here in Aus we can easily pay more than 20 dollars a yard for quilting fabric), but I don't look on quilting as work, so I do not charge my time in that way.
I certainly would not be selling any quilts I make though, because then I would start to think about my time and what it is worth and then I would just start to feel bad about the whole thing.
If I keep the quilt or give it to someone I love, then the payment for my time is knowing they like it. Plus, I put a lot of effort into making things unique, so I know I have something no one else has in the whole wide world- pretty special.
If I keep it, I get to enjoy it and show it off, and that is worth more than any money to me.