I would think that's a plated cylinder, so any cylinder damage is at least a $265 cost plus piston, rings and gaskets. With that being said, it is possible that it only needs rings. When I rode bikes, several of my friends would buy new bikes every 3 to 5 years. The SOP for all of us was new piston and rings about ever other year and just new rings the year between. This was just part of a preventive maintenance routine that seemed to work well. I bought a used KX250 "needing a topend" that I had to have replated and when I sold it 5 seasons later, the cylinder was as good as new (I replaced the piston and rings before selling, so I know the condition of the cylinder). I doubt that would be the case here. It's not logical to sell a bike for several hundred less than it would bring if it had a set of $50 rings installed. I've bought many non running bikes and learned to plan to replace everything, not a cheap and easy item. If he's sure that's all it needs, ask him to pull the cylinder and show you.
