If there's one thing to learn from this thread, it's that the economics of bike commuting varies greatly depending on one's situation. In many cases, it's cheaper than driving, but in other cases, it's more expensive (especially when opportunity costs are considered). I think most of us here can agree that biking is more fun and less stressful, but that's a selection bias because we're reading a bike commuting forum. If it were a driving forum, the attitude about biking versus driving may be the opposite.