WASR-10s are - as mentioned before, routinely built by Century Arms. Thus, it is a bit of a crap-shoot. As Obin mentioned, you stand a decent chance of getting one which is okay, and might just have a few small issues.
$379.00 is a mediocre price, but guns now days are silly anyway. Another option is to purchase a WASR-10 as cheap as you can, and send it to a good gunsmith to rework into a battle-ready rifle. There are a few companies which produce better rifles in the $500 range. If you're not picking up an Arsenal, or custom-build, I'd try to find a place where you can return the rifle, or have it "fixed" under some kind of warranty.
I disagree a bit with NoDub's nothing over $500 statement. Heck my AKs now run me more than my uber-expensive AR. Unfortunately mine was expensive because I wanted an AK in a certain fashion - which they don't sell, so the modifications to it were expensive.
A reliable, accurate, dependable rifle is worth plenty. Other than the TGI AK which never worked from the get-go, I have not had a single malfunction with any of my AK's, perhaps 2000 rounds through them. Check out http://www.atlanticfirearms.com <- they always have a wide range of rifles in the AK pattern available - just might need to contact them to see who makes certain rifles, as they're a bit skimpy with the details.
5.45 vs. 7.62 is a big debate. 5.45 kicks less than 5.56 is basically as accurate, has better material penetration (barely), and shoots a tiny bit flatter out past 100 yards. However you won't find all the fancy sniper-ammo. Non-corrosive new stuff is .20 per round, surplus corrosive is around .10-.12. The 7.62 is much harder hitting - punches through anything, and is generally more serious than the 5.56/5.45 - but its heavy, and drops like a bowling ball at distance. The AK is a perfect rifle for 300 yards and under. If you want to bipod stuff and plink steel at 500 yards, you'd be better off with an AR.