How much is an old SKS rifle worth?

all that aftermarket crap like folding stocks and grips for SKS rifles are not very good. The rifle will be worth more if he also still has the original wood stock. You need to check the country of origin and the general condition of the rifle especially the bore...if its clean then you are good to go, if it looks like its been shot out or if was never cleaned after shooting corrosive surplus ammo then the gun is probably worthless....from your limited description thats all I can tell you...and there are no "new" SKS rifles, all them being sold are military surplus...so you have to check them out really well, some of them are in excellent condition and look like they were never fired, while others are not worth the trouble of melting them down...