John, please tell me you made the speed shop pay for the damage.
Peaches, don't worry so much about the boy and a beater. If it breaks, he can fix it - all guys should be able to fix beaters and it's your maternal duty to give him that essential experience in life, which can only be gained by OJT but is expected by all future wives.
If he's gonna go in the AF, definitely wait. Military guys get good discounts at local dealerships (local to a base or academy) and he could get one himself after he's in the Force with that guaranteed paycheck coming for 4 years. Then you'd be free to get whatever you want and not have to worry about having him on the insurance for it.