I feel the key is a LIGHTWEIGHT bike - CORRECTLY SIZED for what he wants to do. He is small enough to really rip on an aluminum frame without breaking it - and there are quite a few out there that aren't "too" expensive.
I've seen some pretty good bikes in your price range and below from GT and Haro - and obviously there are tons from the "custom" frame companies, but you'll likely get out of your price range.
I suggest checking out PHKBICYCLES.COM
I just bought a Standard STA OX from them and they are the best folks i have dealt with. I've had to ask a ton of questions, since I am from the old GT, Hutch, SE, "Rad" days. PHK answered ALL of my questions, where many other guys wouldn't give me the time of day. (I was even calling bike companies themselves)
They give FREE SHIPPING on anything over $250 - and no tax, so you can save yourself a chunk of cash (save $40-60+)
And, their prices are better than any other places I've seen on the web, and they completely smoke local shop prices.
Keep in mind that the triple wall rims, 8+ pound frames, massive cranks and all this other beefy stuff is mostly for bigger guys. He may struggle throwing a tank around - so I would put weight at the top of my list - but not a racing frame, unless he is going to race bmx - the dropouts won't protect his freewheel and the geometry will be wrong if he is into street riding.
Another option? Ebay. But be careful who you buy from.
I've seen PK rippers in your price range, as well as some others.
But for new biks, PHKbicycles all the way.
Hope that helps.
Standard STA, Hoffman EP Pro
X-owner of: PK ripper, Redline, GT