Driving to work (about 14 miles each way) for me costs about $8 a day for gas alone. If you factor in the cost of the vehicle, regular maintenance and repairs, it's more like $14/day. Add insurance, registration, etc. and it comes up to about $17/day. Now, this is over a 10 year period.

I spent $350 on my commuter bike. And about $700 on clothing, lights, fenders, saddle, rack, panniers, etc. ~$1,050 invested in the past 12 months. In the past year, I've commuted by bike on average once a week, so it works out to about $20/day.

I certainly don't plan on spending $1,000/year on the above mentioned things - probably more like $150-200 for tires and other things that wear out. So, basically, if I continue my trend, I'll break even in a few months, and after that it'll start to become worthwhile from a financial standpoint.

If I were to commute everyday, though, things would certainly be different. I would probably go through 4 sets of tires every year, which would cost about $300-400. It would work out to about $6/day for the first year, and about $2.25/day each year thereafter, assuming the bike frame, wheels, and clothing hold together.

Total daily cost would be right around $3.00 over a 5 year period...again, if I were to ride every day. Maybe my math is flawed, but that's definitely cheaper than driving.