It is a great grinder. What it is worth is partly what comes with it and how much it has been used. Looks pretty new, so that is good. There may be other tooling arms and wheels, which will add value. If not, remember that yu will have to buy them. At a minimum, you will need a flat platen.
Vacon is the maker of the drive unit. IIRC, they make good drives.
I would offer 70% of what they are asking and see where they come back at.