WEll it's really all relative. How much are you willing to pay? Theoretically, if you took the bike and had tires and tubes put on in a shop, it would be a good $200. So you can knock that price down to a G. Now, what else has been done to the bike? Chances are it wasn't running the entire 35+ years it has been around, unless it has a million miles on it (give or take), so at the least it has had a good set of plugs and a carb clean, maybe more. Ask what all he did, and start throwing that into the "time" table. It may be worth it, depending on where you are, etc. These things are getting harder to find for a good price. That's why I always start with the complete pile of shit rust buckets for $100 and spend HOURS getting them running, only to tear them down and start over again. Again, it's all relative.