what is the point of a new car or a warranty if you plan on voiding/ruining it with aftermarket parts? The only reason I would, personally, buy a new car is for reliability(stock) and piece of mind(warranty). If i want to build a car then something cheap and used would be the only route.
If I had to pick something new for the 16k price range, I would probably wait until I could afford more or buy used.
Jimmy