According to APTA, the American Public Transportation Association, the average commuter spends only about $800 dollars a year if they use public transportation, while those who drive can spend around $3000 a year.
Personally, my bus pass is about $50 a month when there's school, and it's about $100 when there isn't. So estimate that their calculations are right to my standards. I spend around $800 a year.
You can actually calculate your expenses on commuting on their website with their commuting calculator.
What they don't mention though is the benefits of driving... I predict that it will be difficult for me to get a job since I don't drive and I don't have a license. You don't have to stand out in the rain or freeze in the snow for forty minutes when you're waiting for a bus. You don't have to worry about lugging groceries or other goods along with you when you have a car.
And if can guarantee that if I had a car, it would be a lot easier to get my cat to the vet a lot easier...