You might try to look into the saiga rifles, they are sporterized but can be converted to an ak style rifle for about 150$ and the rifles only run about 350-400$. Also you might look at the ak's over at centerfire systems...can't say I recommend them, they are put together by idiots but they are alright, after ffl and shipping you could get a low end Ak for around 550$
Yep, that train left the station. WASRs, M10s, AMDs, SAIGAs, and a few kit-builds are about all that is out there anymore in that price range. See Centerfire and Classic, local funshows for the $5XX.00 WASRs if there are any left. Watch classifieds closely.
Avoid any leftover Tantals you might find as cheap 5.45x39 and "AK74" mags are/have dissappeared.