As with many things travel-related, I imagine the process for cruise bookings in Ireland isn't exactly the same as in the U.S. As MCPayne said, over here the price is supposed to be the same whether you go with an agent or book directly with the cruise line.
Perhaps you can find an agent in Ireland who has a group booking with open cabins. These can offer good rates plus some perks like onboard credit.
Personally I'd find a cruise visiting Turkey and Greece to be more appealing than one from Dubai, plus the flights wouldn't be that long for you. That is another consideration for keeping Corkman happy!