I have been looking at booking with them as well. There is a "global" website (go to the drop down at the top right of the page and change the country to Global from United States.) It will price in Euros. I also noticed that the pricing was higher in Euros than in NOK. Not sure why.
Would be curious to see what price differential you got there. For my trip, it was a couple of hundred different, IIRC, but I am only looking for a port to port booking, not the full trip. I did inquire about a better cabin than is currently showing on the website as available and and was shocked to get an email today with a fare quoted in USD that was twice what I expected. Defintely not worth it, especially since we will on be on the ship a few days. My understanding is that they don't release the better cabins for port to port bookings until closer to the sailing date. Can't really blame them. If I was in their Revenue Management department, I'd do the same thing. Supply and demand, I guess.