we are a family of 4 and when we've gone there have been times it's been a substantial savings to take a much later flight but you're right-you have to balance out the cost of food and other expenses. if you are renting a car is later drop off going to cost more? will there be additional parking costs due to staying after check-out time? it all adds up.
the numbers for this for us would be 2 extra meals per person b/c w/ a 12:40 departure we would eat a heavier breakfast to arrive at the airport at 10:40. even if we did fastfood outside the parks it would be tight to save much more than $50 which I wouldn't find worthwhile to have to deal with checkout/storing luggage/retrieving luggage (if not renting a car). when we did it we were looking at a minimum of $400 or more on flight savings so we would check-out at Disney and do a dayrate lowest category room at the airport hotel. people would either crash out and relax or swim until we absolutely had to head to TSA check-in (and we got snack food and sodas to take/ordered a pizza to the room to save on food costs).
