Yeah, I think it can be fixed for a lot less . . . if the plaster is not too thin, or not weakly attached and subject to delaminating.

I'm pretty sure you can clean it up with a diamond grinder, like this outfit:
Bosch DC510 5-Inch Diamond Cup Grinding Wheel for Concrete
Bosch 1773AK 5-Inch Concrete Surfacing Grinder
I'm pretty sure that outfit would perform well for the heavy removal, but you'll need something flexible, too. Diamond grinding has changed so much since I bought the tools I have, that I can't advise you more than that, without doing a lot of research. I have some stiff diamond on copper on fiberglass disks that would perform very well, but those are no longer made.