I've owned a WASR-10, SAR-1, and SAR-2.
SARs are hard to come by for under $500 nowadays, although I found a good deal on mine for $350 with 6 mags and plastic furniture set.
The WASR-10 is a Romanian AKM-47 clone, modded to fire high capacity mags. You can tell it's a WASR-10 by the lack of a dimple on the side of the mag well. These mods tend to cause either loose or tight fitting mags, and rarely work with drum type magazines. I wont church it up, the finish is utter crap, and the stock is a joke. Still, overall the WASR-10 is a good gun, and will easily shoot 20,000 rounds before it has any serious problems, but I dont recommend paying over $300 for one new.
The SAR-1 and SAR-2 are the 'true' Romanian AKs, with the SAR-1 being chambered in 7.62x39 and the SAR-2 being chambered for the 5.45x39 round. The overall machining quality and finish is far better than the WASR-10. The SARs have dimples on the side of the mag wells like they are supposed to, and thus all magazines will work flawlessly with no modification. In my opinion, the SARs are the best AKs you can buy, a bit part being due to its low pricetag. They generally range between $400 and $500, but if you shop around for a bit you can get one for the mid $300's. Again, this rifle will shoot 20,000 rounds before any serious problems.
Oh, and a note on the SAR-3 in .223 caliber: they are pretty much junk, prone to malfunctions and magazine issues. Also the price for decent magazines is ridiculous. Dont be lured into buying one just because it uses a NATO round.
Hope that helps.