Some models are built in much smaller quantities than others. If possible, you want a car that the manufacturer didn't crank out in massive numbers (say, 5,000 versus 100,000 of a similar model). "The lower the production numbers, the higher the value of the cars," says Allen. "Depending on the make and model, there's a book out there that'll tell you all the production numbers, all the options, how many were made of each color. It's amazing the breakdown you can find. Now, with the Internet, you can find more."