While the article and the auction listing both claim the car is screen-used, I believe they are at best greatly mistaken.
The Ecto-1 props used in Answer the Call were build from 1984 Cadillac Fleetwood hearses, and while the to-be-auctioned Ecto-1 is a Fleetwood hearse, it appears to be the 1990s model, based on the headlights.
Other details that testify against it are how short the yellow beacon above the windscreen is, how far the “pool ladder” on the passenger side sticks out from the side of the car, and the LED light on the back of the roof.
This Ecto-1 may have been a promotional vehicle (though I do have my doubts about that). It’s a decent replica, but I don’t believe it has any film lineage.
Hopefully that means it sells for a lower figure and a GB fan ends up with an Ecto!