Well, we pretty much do it the opposite than you do. The "best deal" is one of the last things on our priority list. The date, the ship, the itinerary are all far more important considerations to us. That pretty well means we don't do any "last minute" shopping.
Our best Transatlantic was on the liner which is expert for Transatlantics, the QM2!!
check out our trip report and pictures at http://www.bully4.us/crossing.html
We loved it! But I have no clue what sort of "deal" we got.
Diff'rent strokes for diff'rent folks