I sold mine a couple of years ago for $400 and thought I did very well.
In looking at GB, it looks like they have sold for anywhere from $250 - $500 so it's your call what you ask for it.
I did the rounds on several gun stores and saw a MkI with fixxed sights and a MkII in SS. Both were used but not abused and both were almost $200, like $198 and I was amazed at that price. On your NIB model I would also start high and hope for a collector who wants one.