You forgot to mention how much fun it is to ride your bike twice a day.

OK, you've sunk two car payments (more or less) into bike commuting. Call half of that hobby cost (you could be sitting in traffic instead of enjoying yourself). Now get set to spend that much more over the next year. If you can put off buying a new car for a year because you're cycling to work, you will have saved 9 months' car payments.