You probably know this already, but your only real option in that price range is a Century rifle. A good Century AK is worth your money. But they also produce more lemons than just about any gun company out there, and nothing sucks quite like a brand new gun that won't go bang.
I would make sure you can either inspect a Century AK before you buy it, or get a third party warranty if you're purchasing online.
One series of AKs that are mostly problem-free are the Yugo PAP rifles, like Hoofan mentioned. They are well built guns and are pretty cheap, but they are a few pounds heavier than a WASR.
Another option is a VZ 2008. They are a Czech service rifle, and the best way to describe them is a not-really-an-AK AK. The guts are different, but you can definitely see where the designers were coming from. It's just as good as any other low end AK, and some owners think they are better than the WASR-type rifles. By all accounts, they are well-made guns and are largely free of the problems that plague most of Century's imports. Palmetto State Armory has a deal where you can buy one with five mags included for $400. For that price, you really couldn't go wrong.
Hope this helps.