Jaime,
You are looking at something like 10-11 hours in the car from DC to Toronto. Assume 5 tanks of gas for getting there, driving around and going back. 20 gallons per fill up times $2.10/gal = $42 per fill up. Five fill ups times $42 = $210. Plus whatever you spend on parking and food during the trip.
If this is a holiday treat/vacation kind of thing, I'll guess you can probably find something on the web for a flight that won't be much more than the cost of the drive, save yourself alot of driving time AND not have the hassle of finding your way around downtown Toronto/manage your car. Most of the stuff you might do would be within walking distance of a nice hotel.
