Greek Error Card

I was wondering if anyone could give me an estivated value to this Greek postal card error?

What the scan may not show is the embossed image of Mercury on the U/L corner. The stamp impression is in the right place but I think that the card was feed in twice in the process of printing it and that may be why the 'albino' impression is also there?

The shift in the overprint is quite dramatic as well.

Chimo

Bujutsu