With 1000€ you could buy a small apartment, rather then a small mask. If you are a rich collector that doesn't care how much money he spends to complete his collection, that go for it. If you are just a regular LEGO fan, you can get like a huge haul of sets for that amount of money. It depends on your budget and how big of a fan you are.
Since the mask was only given at the LEGO Inside Tour, and only 200 of them exist on the entire world I can understand why it's so valuable.