Mallow, my advice for anyone considering that long of a drive to WDW would be to fly, but I am biased. In addition to quantifying the time/fatigue/grumpiness factors for each option, here's what I'd suggest you contrast and compare in terms of potential cost:
Driving
* Gas - (just take your average MPG, Mapquest the total distance and do some simple calculations, assuming the price of gas will probably be around $3/gallon)
* Tolls - you will hit some toll booths along the way
* Hotel - probably 1 night on the way down and 1 night on the way back
* Meals - you'll also need to eat if you fly, but you'll need to cover more meal times on a drive
* Parking - if you use your car while at WDW
Flying
* Ground transportation to/from your home base in PA
* Airfare
* Ground transportation while in Orlando (may vary, depending on how you get to-from MCO and to-from the parks, and whether or not you rent a car)
There are probably some other factors, but these are the basics...If the difference is within a few hundred dollars, I'd say fly, but of course I would say fly anyway. I'd suspect there won't be a huge difference in cost, and I really believe the time you save and the energy you avoid spending on the road is more than worth it for the overall quality of your vacation!!