If your only concern is cash, then plan to drive, but keep looking for tickets. Check a range of options daily. Airtran runs some deep cuts, Southwest occasionally offers friend's fly free deals, etc. I often use US Air and via their web site punch in my flight data but choose "flexible" instead of a given date. Then I see if they have the date to suite me in their lowest price catagory.
Regardless, when it comes to the "cost" of driving versus flying, I've never made the numbers add up in favor of flying, especially when you factor in two extra days of vacation killed.
However, if I have the time to burn, I find driving superior. As you see in these posts, that's a pretty subjective thing. I like dtauer's list, and most anything I could add to it would be suplemental to that list. But beyond the fact we like to see the country, the biggest advantage we see is not being contrained by suitcase space.
We're driving in June (I live in Central PA, by the way) after flying the last couple of trips, for several reasons. My wife has a professional event in Savannah and we figured boy, is that closet to Orlando. She's going to be six months pregnant at that point. Never a fan of flying and doubly scared of it after 9/11, the presence of an unborn child and the situation in Iraq has her saying "hey, I'll go, but I'm not flying." So I'll fly to Savannah (I figure I'm as safe up there as going around the Beltway on a Friday night) and drive her to Florida and back to PA. Before she leaves, I'll pack every blessed thing we own in the back of the car that might be useful in Orlando, including extra coolers (and shoes, we always seem to have to cut down on shoes). I find driving to be an excellent expirience.
The downfalls of driving: Cabin fever (can hit at any time). Road weariness. The ever-fluctuating price of gas (and June's not looking good). Dealing with traffic. And with flying, when you get to the airport, you're almost there....
None-the-less, we look forward to driving. As for blasting down there or taking an extra night, personally I've tried it both ways and we've decided on a third way. Blowing down in one swoop (it's about 18 hours for us) meant leaving at 5 AM and getting in just a bit before midnight. The next day, we were toast, just terrible. The next couple times, we drove halfway, to southern NC. There was something mentally taxing about waking up in the AM and realizing we'd done all that driving the day before and were only halfway.
Our solution, and we've done it twice, is to drive from here to Savannah, GA, which is about 13 hours. We leave at six, we're in Savannah in time to get situated in a hotel, have dinner, and get to sleep at a decent hour. When we wake up in the morning, we're only 4 1/2 hours from Disney. We normally leave by seven AM. Knowing we'll be having lunch on the Boardwalk kind of removes the mental doldrums.
So my suggestion: Bomb most of the way, but have a five hour or less drive on day two. Don't try to blast down there in one shot, your first full day in Disney will be spent watching the paint peel in your resort. My opinion, anyway.
Pat