The only way you can justify making payments on a car in your situation is if you can get a super low interest rate. This is highly unlikely with a used car. You have to look at how much interest you would be paying when you really don't have to. It is like throwing money out the window if you have enough to pay cash in the first place.
My advice would be to buy the car with cash and make monthly investments of roughly the same amount you would have paid in monthy car payments. This pay yourself philosophy will net you more money in the long run.
Ed
