Guy came and bought my car last night.  Goodbye little Nissan Altima.  In the end, here are some of the stats:

Years owned: 10.2 (15 total years old)
Mileage I put on it:  138,000 miles (197000 total miles)
# tanks of gas: 424 (approx)
# gallons of gas: 5520
Cost of that gas ($2 avg): $11,040
Price of vehicle/years owned: $945/year
Cost of driving/owning per year (vehicle+gas cost): $2049/year
Insurance+repairs would have been about:  $1200/year

Cost of driving per year = $3249

So when your teen comes wanting a car, put this figure in front of him/her and see if they want to put that kind of money down per year.