well - apparently - depending on extras (high resolution module etc) it would have been worth around £50'000 when new.

However, that was 5 years ago - which in 3d printing terms is about 20 years in normal development terms.

So a comparable size and quality dlp resin machine could probably be had today for a few thousand.
It would appear to have an unusual wavelength - so one thing to look at is how easy it is to get the resin and what that costs.
Assuming you can still get it.

What's it worth ?
Sheesh - how long is a piece of string.
Probably anywhere from £1000-5000.
Depending on what the buyer knows.
And what resin it can use.

I can't imaging anyone paying more in the current climate - as you said yourself, the formabs form 2 and the new larger sized machines probably do a better job.

Good luck :-)