How much should I charge for a mural?

The owner of Tuffy's auto service shop called and asked me to redesign their front desk area. That includes 2 walls. He wants me to paint a mural. He said that he wanted the shop to be on the mural along a highway. I sketched up a highway and alongside it is tuffy's then on the other side is another car shop that says "OUT OF BUSINESS" in the window. Above that says tuffy's moto: "nobody beats a tuffy!" Do you think he will like it? Also, how much should I charge him? Keep in mind the supplies I am going to need.