We're about a 21-hour drive from Disney (NY state). According to the "driving to Disney" website, it would cost us about $420 in gas to get there and back (and that doesn't include the cost of one night's hotel or campground stay each way, unless we decide to do the whole trip in a single leg, or pull over and sleep the four of us in our SUV at a Wal-mart parking lot. We're so hardcore.) Given the fact that we have small children and don't own a vehicle with reclining seats, I'd go ahead and budget $100 each way for accommodations.
The cost for roundtrip airfare on Jetblue or Southwest from Rochester/Syracuse/Buffalo to Orlando is $1,200 max for the four of us.
So driving would save us, at most, $780 (if you subtract $200 for hotel, it would make our savings more like $580). That's a nice chunk of change, but when you consider that we're "losing" a day from each end of the vacation, it's not worth it for me. DH and I only get 2-3 weeks of vacation per year, so every day is precious, and although we do enjoy road trips, we'd just rather spend that extra time in Disney World. Not only that, but I already spend well over 2 hours in my car every day, between a long commute to and from work, picking up the kids from daycare, etc. I'd rather not spend too much vacation time in there!