If they are a mated set I would say LOTS. More than any new aftermarket gears for sure. 3.55's aren't available from any aftermarket mfr and these are new GM. It doesn't get any better than that. Couple that with the fact that 3.55 was the std ratio in many Chevy muscle cars and the high demand for that ratio today. If not a mated set they are worth next to nothing IMO. That's the big question, how can he tell if they're a mated set? If you go by the date on each it doesn't look good.