Anywhere from $200 - $400 for an M59/66 (model with the grenade launcher attachment, gas cutoff valve, and flip-up grenade sight), with $400 being for an unissued rifle with all accessories.
$150 - $1300, depending on specifics. You could get a non-matching Yugo for between $150 - $250, whereas the much rarer North Korean SKS would be closer to the $1100 - $1300 range.
Depending on what shape the gun is in and what part of the world it was made you can expect to pay in the low 200-280 range anything more you are getting ripped off. the sks can be a good buy and can...