I wrote them an e-mail about one year ago - at that time the double version was 650 Euros plus some 50 Euros shipping (within Europe). There was a slight price increase then, but that was a few months back, I don't know what the current price is.
The price was stated somewhere on their website at that time. Or at least in a document one could open/download from the site. I've just taken a look at their website and haven't found any price indication this time though.
Just e-mail them for a price quote, and come back and tell us here ;-)
There's a thread on those pedals on Derek Roddy's website, too, but it's more of a "do you know those pedals?" type thread:
THE DEVIL's HOOF amazing looking pedal from Poland!