I wouldn't go as far to say Airsoft is not for him if he can't/won't blow $500
You just got the budget your stuff, and find deals. Being Age Verified REALLY helps.
If you're into airsoft (Been to a game and like it) you can pick up a decent gaming rifle for ~$200 ish.
Sure you might need it upgraded/fine tuned/worked on after sometime, but that's not overly expensive especially if you do it your self.
Mags can be had cheap ish $100 or so.
See if you can borrow/rent a battery from somebody. That will save you from buying a good charger and batteries off the start but you really should invest in those sooner then later.
Buy a few belt pouches or a cheap vest to hold said mags. Throw on a pair of boots are you're golden.
Goggles are nice as most places who rent them don't have overly great quality but they will do, or ask and see if somebody can lend you one.
You can pretty well get a small basic load out for under $4-500.
After sometime, upgrade here and there.