If the OP's buddy wants a semiauto, he's not going to buy a shotgun or revolver no matter what some dudes on the Internet say. I was a new shooter not long ago, I would certainly recommend a 9mm, good all around and cheap. Plus why would a new guy want to buy used? Maybe he could find one, but would he even know what to look for? Be realistic, it'll probably be new.
So...doing a search over at buds for semi auto 9mm's, you really only have a few choices under $400. You'll probably have a FFL fee of course, so these may push a little over your mark. But here goes:
S&W Sigma
Ruger P89
Taurus 24/7
Ruger SR9
Of those, I've only shot the Ruger SR9. It's a fine gun and fits a lot of people. That'd be the first one I'd look at. The 24/7 has lots of good and bad press, but generally it seems well regarded. Never shot one, nor a P89. You've heard the other guys recommend their Sigmas, so take that FWIW. Any of them'll work fine. Again, if it were me, I'd do some searches on the SR9 and 24/7. I'd probably go for the SR9 if it were me. Good luck.