If you browse gunbroker.com, you can see the HIGH side of their selling prices. Much depends on the condition and model. I think i paid about $325 for my pre-bubba'd Chinese SKS with the ~20" barrel, last year. If it had been a -M or -D that uses AK magazines, you could add a couple of hundred bucks to that.
I'd check the going price on some auction sites; gunbroker has a GREAT variety and usually has good pics, but the prices usually seem a bit high to me.