A WASR-10 will be your best value. I'd say it is the standard in the AK community.
http://www.atlanticfirearms.com/comp....html?Itemid=0
The N-Pap's are a good choice, too. Just know that it won't take certain aftermarket parts. For example, if you ever want to change out the furniture, you'll need Yugo-specific handguards and stock.
http://www.atlanticfirearms.com/comp....html?Itemid=0
I happen to have one of each, although my N-Pap is the underfolder variant. I bought the WASR over a year ago (when they were over $100 cheaper) and haven't even shot it yet. Didn't find anything wrong with it during the initial inspection and cleaning. I have shot the N-Pap, and its good to go. Very accurate for an AK, but takes some getting used to shooting an underfolder.
And as people have already said, you should also consider an SKS. They are usually cheaper than an AK, fire the same ammo, and operate in similar manner. I actually prefer the SKS, which is why I have 4 of them! I've found them to be a bit more accurate, and much smoother shooting. Not as much felt recoil in my opinion. A functioning SKS in good condition with the original parts seems to be going for $300 - $350.