This was my first thought... 9mm easy on the wallet and the shoulder....mags are plentifulSomething like a Ruger PC Carbine is worth considering as well. If he gets a Glock or a Ruger SR handgun at some point he'd have magazine and ammo compatibility. Higher capacity and cheaper than most of the pistol caliber leverguns as well (Rossi excepted).
Another question to ask is what's his budget?