Now when your looking for a car to represent the highest being known to exist in the universe, theres really only one choice; the highest being known in the car world.
Here is the 1000+ HP 16 cylinder Bugatti Veyron SS which, is quite frankly the Concorde of the car world. In fact the Cosmic Nerds's cars would not exist if it were not for the Veyron setting the benchmarks they needed to achieve and surpass.
This one features Bahamuts colors as well as his head and back rugs and the gold band around his tail on the Veyrons wing. I say it fits him to a t.