I'm not sure, but it has to be a lot. I don't have a car at all, so I don't pay for insurance, registration, or gas. I don't pay for college parking permits, either, and the vast majority of maintenance I can do myself. If I do pay a mechanic, it's much cheaper than if it were a car. I do use public transportation, but my college gives out county bus and light rail passes, so I'm only paying the $5 transit tax the college charges every quarter. If I want to go to San Francisco, it's $7 in train fare each way and $2.25 per 90 minutes for public transit. If I want to go to Santa Cruz, it's $5 bus fare each way and a bicycle gets me wherever I want to go in style.
All in all, my transportation is extremely cheap. I would not give it up for a car.