Hi Roi,
buy it? Are you kidding?

The owner should give you a few bucks, if you take it away from his yard...
I just looked at the other pictures. There seem to be very few parts which are worth to "plunder". Maybe the frame is still good (but I doubt it). The running board could be OK too, as well as some minor spare parts. But as a whole this scooter is from my point of view basically scrap metal.
Nevertheless here at the Heinkel Club we consider all Heinkels to be "objects of major cultural value" - regardless of their condition. So, if you can salvage this wreck (at no charge would be best) it could be worth to save it. There will come a time (but presumably in the far, far future), when Heinkel spare parts will be precious. Today (and hopefully for a long time coming) you can get almost all spare parts for reasonable prices and in very much better condition from the Club.
So my advice is: get it for free and stow it away or forget it (and care for your 150).
Kind regards,
Bernd