We drove to Orlando a few times. The first time it was 5 people, spread out over 2 days. We started out at the Carlisle interchange off the PA turnpike and took one of the main highways there. It was a very nice drive actually, very scenic and best of all bypassed Washington D.C. and all of its congestion! We eventually picked up 95 around Atlanta.
The 2nd trip, my wife and I took 95 straight down, we left 4:30 am Sunday, drove straight through, only stopping for gas and a quick packed lunch at a NC rest stop. We hit Jacksonville, FL, 6:30 pm and stayed the night then drove to Daytona the next morning.
On the way back, we left the hotel at 8:30, drove straight through and got home to Boyertown, PA at 1:30 am. 95 around DC was terrible that time of night on a Thursday.
Price wise I figure the drive costs the equivalent of 1 airline ticket. Gas is expensive now, and with our car I figure 3 fill-ups for the 1000 mile trip. Plane tickets right now around fairly cheap, usually costing $170-190 a person from Philly (just got 3 round trip tickets for July on US Air for $530).
But if you plan on staying awhile and renting a car, car rentals can get expensive, so when you factor in that expense you save more $$$. We hardly go outside Universal (since we rarely get to go longer than a few days) so we don't need the expense, just transport to and from the airport.
Good luck with the drive, let us know what you wind up doing.