Wow! I don't think that I've ever paid that much for materials for a quilt! First, to cuts costs, you might want to rethink your materials. There are a lot of great sales going on at the online stores, so you might check those for fabrics. Also, EBay has a lot of vintage fabrics for sale with a cowboy theme, s/a prints, denim, bandanna, etc. You could also use some of your scraps and just fill in with the novelty fabrics to cut down on costs. There's always a batting sale out there somewhere too.
As for labor, I would charge her a straight, per hour fee...whatever you think that your time is worth. Personally, I wouldn't do one for less than $15/hr., unless it was for a family member or close friend. Those would be for free, of course.