Being young and needing reliable, safe transportation, I'd recommend getting a track only car. A Miata, Mustang, whatever that is very plentiful and cheap to drive, fix, repair. If he damages the race car, he's not out a daily driver. You can pick up a very well sorted car that already has all the safety equipment, extra parts, etc....let somebody else spend all the money getting a car ready and pick it up for much less than if you did all the work.
Being a track only car, you don't have to pay insurance, license fees, etc. I'm guessing that full coverage insurance on a newer WRX for a teenage boy is about $5000.00 per year. Add another $5k and you can buy a very nicely sorted out race car. Something like a spec miata, showroom racing or IT class car would be ideal. Stock enough to be reliable but with the correct safety and track equipment already done.
Then he can use a very reliable daily driver with awd that has the capability of towing the race car. Let him drive a couple of years on track with the track only car before allowing him drive his daily driver on the track. Hopefully after enough track miles, he realizes that there is nowhere on the street that he can approach the speed and capabilties of his car like he can on the race track.
You need to be very careful, fast cars and young boys can often end up in big trouble. Having a cool daily driver and a dedicated race car to brag to friends about could be the answer and save money and future street racing tickets.
Good luck, your kid is very lucky to have a dad willing to put him on the track.
George