Yeah, I'm going to reiterate what Jason and Kris pointed out. We each have different styles, techniques and price guidelines. For instance, Jason is very successful with traditional drawing methods, Hickman, McBride and I seem to have a mixed media method using some traditional methods and some CAD(photoshop), and everyone knows Kris' unique 3D CAD style.
When someone contacts me looking for just a paint scheme and wheel upgrade, I like to photoshop a hi-res photo. It's quick, relatively easy, less expensive for my customer (depending on # of variations and graphic complexity) and you get exact proportions and lighting. The down side is that you are limited by the quality of the image received from the client. That's why I like to offer both methods. Here is an example of something I worked on for a Camaro enthusiast magazine a couple weeks ago. You can see what I started with in the inset photo.
I'm sure one of us can do exactly what you need.
Good Luck!
Ben