I think the airlines know most schools in the northeast are out that week and are looking to soak those that travel to Florida.
I have travelled on that week for the past several years and here are some alternatives we have done, but I must say even these suggestions dont yield the massive results they used to:
1) If possible fly out of airports where the local schools dont get off on Presidents week (basically many NY and New England schools have off) so we have flown out of Allentown, Philly and Baltimore to get our WDW fix on Presidents week
2) In the past Orlando was most expensive, but places like Tampa were less so. So we have flown into Tampa. This strategy seems to totally not work anymore
3) If all you need is a Disney fix, you can fly to LA and goto
Disneyland for less than flying to Florida on Presidents week. DL is really great and I recommend it.
4) Be flexible on the dates you fly. If you wait until Sun or Mon to fly down to Florida, it may be more reasonable.
5) Drive to Fla. Ugh, I hate this option.
This year will be especially challenging for me as we are taking the Disney Fantasy, so we must be there from at least Saturday to Saturday... American Airlines is around $375 round trip. I may actually have to bite the bullet on this one...