As far as making custom body pieces, my buddy has had great luck over the years by using sandwiches of rigid composite building insulation board glued together to form the flares, air dam, whale tails, etc, then after using sanders to shape it close, he coats it with a release agent and he uses a fiberglass chopper gun to spray fiberglass on it and make molds.
He bought all the sheet metal for the last generation RX7 and made his complete body for his SCCA tube frame RX7 from molds he made with the gun, and then of course, uses the gun to make the body. Some people have more time and $ than others though. I guess I'm an under achiever!