We drove when we went in 2008. We are in London, so only a couple of hours farther than Windsor. We spent about $800 in fuel, food and hotels for the trips down and back. That was also for driving a truck in four wheel drive for a good portion of the trip down as a nasty snow storm hit SWO and upper states Friday night and Saturday. We changed our plans and left Friday right after school because of the storm so we had an extra hotel on the way down too. It was cool to drive as it was the first trip to WDW for my DH and DS and they were looking at the scenery as I drove. MIL gave us a cool trip book called Along I75. It is a 25 mile per page map that lists exits, attractions, restaurants, gas stations, hotels, etc. for the entire route. It was really neat to have as DH was able to point out interesting stuff along the way and we could plan where to eat, fuel up and knew what hotels were coming up.
We are going again in 2012 and the whole family is coming. MIL and FIL will already be down there as they go south in February for Daytona (they drive). BIL, SIL and two nieces are coming too and we plan on driving as it is their first trip down I75. We plan on getting an updated I75 book for this trip. For us, airfare is too expensive. Flights are over $3000 if we fly out of a Canadian airport and just over $1600 if we fly out of Detroit (including parking and gas to Detroit and back). The cost difference makes it worth it to drive and we don't mind the extra days as we plan it that way.