For a second-hand one from a private seller you used to expect to pay between 200 and 400 GBP depending on age, condition and particular model. I bought one last year (red with grey roof and back underframe, old style split gearboxes) and paid about 240 GBP for it. But, as you say they seem incredibly scarce now, even German eBay hasn't got many and those they have seem to be at very inflated prices. I did find this one, with early (analogue) sound, at a BIN price that is still quite high but less than some of the others:
http://www.ebay.de/itm/LGB-2096S-DI...dellbau_Modelleisenbahnen&hash=item20b9edbc2e < Link To http://www.ebay.de/itm/LG...mp;hash=item20b9edbc2e
I've used this particular seller before, he seems decent and honest and ships worldwide.
Even Grootspoor aren't listing any 2095s at the moment, second-hand or new-old-stock. Basically, if you want one and see one at anything that is within your budget, grab it!
I can't believe that Marklin won't re-release this one eventually, it's such a classic LGB favourite and they do have fairly modern toolings for it (from the most recent orangey-red one with the cream roof).
Jon.