Did you pay (or are you paying) his way to college? If so, enough is enough. You don't need to buy him a car. I'd maybe think differently if you could do it without financing, but at this point it's time to think about your own future.
+1 If you don't have the money to pay for it without financing, you are not wealthy enough to buy him a car as a gift. Your gift to your son will be your ability to support yourself in retirement. If you become well to do in the future, you can help out any grandchildren or you can insure your son's retirement security (which is looking like it could be an issue for the millennials). A car is not the kind of asset you should be thinking about for your son's long term well being. Does he need a car to get to work/does he have a job yet? He might get a job where he can use public transit and the car would just sit there anyway. Wait to see how you can best support him with his future plans after college.