This 1959 Cadillac Miller-Meteor ambulance, converted by Universal Studios into the Ghostbusters' Ecto-1, was up for auction on eBay. The listing does not imply that this was the one used in the movie. I'm sure there were several made for the film and other promotional uses. The high bid was $45k but did not meet the reserve. From the auction listing:
There is not a lot that can be said about this car once you see it you know what it is. This car was owned by Universal Studios as you can see by the copy of the title. This is the real Universal car not a copy. The car runs and drives good it has new tires on it know. The car is in a car Museum right now, when it goes on tour it draws a VERY VERY LARGE crowd.Ecto-1 on eBay (via Laughing Squid)
David Pescovitz is Boing Boing's co-editor/managing partner. He's also a research director at Institute for the Future. On Instagram, he's @pesco.