I'd go for an E36 four-banger. Much power is just not good for a starter (wich I understand your son would be out on track?). Those four-cylinders are very well balanced cars and are really fun to drive. Fact is, you learn to drive a clean racing line because you do not have the power to make up mistakes on the straight line. If you're fast with a 320i, you're also fast with an M3. On top of the learning curve, parts for an M3 are more expensive (so, in Germany, maybe in the states they're not). M3 = multiplicator 3.
Same for the E30s. They are really fun to drive, easy to work on and there are whole lots of parts available. At the end, you can always swap in an M-engine in case power becomes an issue some day.
So I can tell you from the Nürburgring, those cars can be seriously fast with a talented driver behind the wheel and you see a lot of them there.
Last edited by MEHP; 12-12-2011 at 05:44 PM.