The yugos are everywhere. Expect to pay between $180 to $250 depending on how greedy the seller is. Check the internet for importer's pricing. The yugo's that have the grenade launcher on them are heavier. I don't care for them. They have the advantage of being able to turn the gas operating system off and using them like a straight pull bolt action. Depending on your interpretation of the BATF laws, removing the grande launcher removes Curio and Relic status of the firearm making it illegal - I am still researching this, so don't take this as gospel. If you want a lighter weight gun, get one with out the granade launcher.
Chinese Norinco's are nice. The ones with the chrome lined bores are abundant. Without the chrome, check for bore condition. Learn disassembly and check the operating rod for damage and cosmoline. Most vendors won't mind you taking them apart to inspect. Check the firing pin for gobs of cosmoline also before shooting.
The Russians are generally thought of as "better" made. They all work the same. Collectors pay more for the Russians, so watch pricing. I've seen them advertised for $400. Not sold, just advertised.
Good luck and enjoy the show! zcarp2