from the graphics I am guessing it is approximately 10 years old. Is the seller willing to sell the frame only? If not, what are the components? Is it campy or shimano?

Another option--check e-bay. You can find colnago frames and get a sense of what they are selling for.

One thing to be aware of w/colnago--the paint tends to chip off rather easily. If that is the case with this bike--check to see if the owner patched it up. (On my steel colnago I have patched it w/dabs of bike paint and nail polish to prevent rust). This is just to ensure that there is no rust.

I am not sure what the going rate for a used colnago is in Europe. So, find out what year the bike was built and whether it could be a frame only sale.

Honestly, if I were to sell my 2000 colnago classic (frame only) I would ask $500 USD to start (as it is well maintained, no rust, etc.). The Master is the "next step up" in the colnago line so could get more depending on the condition, etc.