Some fitting may be required on the part of the stock that protrudes into the receiver depending on what the stock was intended to fit, as Chinese and European AKs are slightly different, but you should be able to make either work with few exceptions.
How much do you want to spend? Vector Arms sells their underfolder AKs (which with an underfolder you won't be able to easily swap on any AK yourself, requires a specific trunion and several holes in the receiver) for $500, Vector is supposed to do a real nice job...
Ohio Rapid Fire offers some side folder AK74s (the type of sidefolder that is generally more "desirable" as it's rarer and also requires a specific trunion, etc) for somewhere around $600 I believe.
The cheapest and easiest method would be to get any of the Romanian AKs that sell for $300ish and swap on a Romanian sidefolder rear stock, easily get one for under $50 and they drop right in...
There is also the Tapco sidefolder for somewhere at or under $50 too, but they're not milspec surplus stuff, made mostly of plastic, I question their durability (but I don't have one...)