Because you have a car in the first place, I wouldn't be surprised if you don't reduce your dependence on it at all. I live steps from the subway in midtown and have a car because my job requires it. Because I have to have a car anyway, the incremental cost of using transit is huge compared to driving.
Gas works out to 10 cents a km. Because I live central to friends, family and all the places I shop at, I only drive about 200 km a month for personal trips, which costs 20 bucks in gas. The TTC would cost 100 bucks a month with a metropass, for an additional annual cost of about 1000 dollars. I should mention that parking is always free when you know where to find it.
While I would happily leave my car at home for 95% of my non work trips, I end up using it for 95% of my non work trips because the TTC costs a bloody fortune when you only travel 1 km at a time.