if it's been sitting out in a field for 3 yrs then i wouldn't bother but $100 for an engine you'll be rebuilding is not too bad to use for spare parts at least. you'll have to buy a frame anyway so it might be best to wait for a more complete bike. i bought a '75 CB750 for $300 that was missing the carbs and exhaust but the engine turned over, it had 21500 miles on the odo, never been opened and i bought it from the second owner. i thought it was a good deal but many here will tell you not to buy a bike that is not running. have you tried craigslist? there are a pretty steady stream of CB's on my local craigslist but i don't know where you are located.