If your building the car, start with deadener. Read up on this website, and shoot the guy an e-mail he is awesome at helping you obtain your goals, Sound Deadener Showdown - Your Source for Sound Deadening Products and Information. He doesn't even care if you use his product or not.

Next I would look into an active set-up. A 2-way front stage with a single sub should be more than enough, especially if you got a good processor. You could get all the speakers for fairly cheap, a processor is where your money will be at, but will make the world of difference.