There are lots of hidden costs to florida, and not only is there food, entry to theme parks, travel the little ones will also want things from the gift shops too which is really all part of the experience...
If his heart is really set on taking them away why not to disney in Paris for 4 day break? No jet lag, cheaper in long run and not so far for little ones to travel.
I dont know your situation but i do undestand that it is hard letteing xp have them.. On the flip side (and i stress i dont know your situation) they might really enjoy it and re-inforce good bond with their dad.