Can the cars be bought online or do they come to your physical shop to buy the cars?

If so, you could set the cars as Call for Price which will allow you to post a price if you want and flag the car as Call for Price and not allow it to be added to the shopping cart ...

If you want them to purchase the cars online, then you would need to customize a shipping module or set the weight to 0.00 or set the car up as a Virtual Product so that it does not aquire shipping ...

NOTE: being a Virtual Product means it will not show the checkout_shipping page ...