How to choose a guitar? That's a matter of personal preference. If you've never played one or you're a beginner, all you really need is something that works. Later on, when you know what you're doing, you'll know what to look for. For cheap and basic, nothing beats taobao.
I just got a new stratocaster copy on taobao from these guys:
http://trade.taobao.com/trade/detail/tr ... 6469750968Only 205 rmb. In spite of the price, it's actually one of the most well balanced instruments I've owned. If you're looking for a dread knot acoustic or a classical guitar, you'll find plenty of those too.
If you want to try it out in person before buying, most shopping mall music stores sell "Blast" brand acoustic guitars for 200-300rmb. They're not awesome instruments, but they're great to learn on. If your son really digs guitar and wants to keep it up you can always upgrade from there.
You'll probably get a bunch of recommendations to go to Jingling Road which has a ton of music stores with quality imported merchandise. However, you usually don't find the cheap stuff there unless you ask the store managers where they hide their locally made instruments not on display.