There’s no telling what “all the labor intensive jobs are done” means. Specifically, what are the component times? If you’ve gotta throw in overhauled components such as blades, drive train, engine, etc., you’re easily looking at another 150K. And you still have a 1980 Enstrom.
The seller’s comment of a new 750K Enstrom is meaningless. It would be like trying to sell a 1980 Baron project and saying that a new one goes for 1.5 million. Who cares? Your project is far from being completed and far from being new.
Personally, I’d rather buy a late model 280 with nice paint and updated panel for less than 200K vs buying an old project and sinking a fortune into it.