My car has an 18gal tank and only runs on premium - I've been over $4/gal for a while. Luckily, I've only had to fill it 3 times this year. The rainy weather and my wife's changing schedule resulting in me having to get the kids to school has made it harder to bike commute every day recently.

Bike commuting wasnt cheap at first, but the cost has dropped drastically this year. I have 6-8 tubes I patch and rotate. I have all the winter gear I need, lights, etc. My main expense is a new chain and tires every 3000 or so miles. I guess I could go to a single speed commuter and could probably go a few years on a chain. Car tires are way more expensive than bike tires - plus, I only need 2!