I think value is probably going to be more a case of what it's worth to your self.

To build a similar spec machine, it'll probably cost you over 1k. I'd probably say the base machine isn't too far away from something like a X1, which would cost you £5-600. It'll only likely have some pretty basic rolled (C7/9) ball screws, which would probably cost you another couple hundred pounds, plus motors, wiring, and enclosure.
I wouldn't include the controls, as most of that is obsolete so it's not really worth much.

Personally, if it was under £400, I'd probably buy it regardless of condition.
£4-600, if I knew it was mechanically good.
If I needed it and the location was convenient, I might pay more, as moving even small machines can cost quite a bit of money.
It might even be worth paying more as it's got an enclosure, which for some people will be quite useful, and would be fairly expensive to build.

Certainly over £1k, I'd be looking for something from Denford, as they are better machines.