Happyhunter: If you are not looking to break the bank and I assumed from your posting you are not, then there are a number of used 9mms out there that would satisfy your son's desire for a 9mm to plink and shoot.
My preference would always be for the Browning High Power - you can install some very nice sights very easily; it is a single action auto and you can easily obtain match grade drop-in barrels in 9mm that will make it a real target shooter. I also love the Walther P-38. A lesser expensive idea is the Tokarev in 9mm, and from there I would look at High Power clones, used Beretta's, used Smith and Wesson Model 39/59 if you can find them. Hope this helps. Mikey.