Asking prices are one thing but not many are changing hands for that sort of cash - a fair bit less than half that would be absolute tops, and you would have to wait a long time to get it.
Anything at the right price doesnt makes it to Ebay or Gumtree anyway, so these sort of sites are not a realistic guide to price.
A good R100 GS can be had for about a quarter of that, excellent K bikes are almost given away, a couple of grand gets you your pick, and a little more will get you and early oil head GS.