While in terms of quantity the numbers are quite low, with so many other new event rares coming out that are also in the single digits if not unique the value of these items is really going to be dependent on the buyer and how desirable they find them.
With an item such as this that has a hue that I don't believe is unique or in other words can not be created via other in game means, and with a name that is well shall we say a poor choice what with the suffix I would value it at about 1/3 to 1/2 of what you are estimating, basically 50-75m.
Just my opinion of course, there could very well be someone out there who would really like a +4 pirate slaying axe
