The one study I've seen that looks at the net health effect of cycling came to the conclusion that cycling is a net benefit. Loads of bicycling advocates promote this to suggest that cycling is in general a net benefit for you health. Unfortunately for North Americans, the data in the study came from Europe. Cycling is much safer in Europe. I am not aware of any analysis using data from North America, and I'm unsure whether such an analysis would come to the same conclusion.
With this being said, I ride a bike for transportation. I read studies on safety and actively try to minimize my risk. This includes minimizing my mileage, as the risk is per unit distance. So far, so good. I haven't been in a real crash yet in 4 years of commuter cycling, though I've had plenty of close calls. Worst I can say is that I did once hit a pothole and fall over, but there were no lasting effects.
On ChrisHallquist's post extolling the virtues of money, the top comment is Eliezer pointing out the lack of concrete examples. Can anyone think of any? This is not just hypothetical: if I think your suggestion is good, I will try it (and report back on how it went)
I care about health, improving personal skills (particularly: programming, writing, people skills), gaining respect (particularly at work), and entertainment (these days: primarily books and computer games). If you think I should care about something else, feel free to suggest it.
I am early-twenties programmer living in San Francisco. In the interest of getting advice useful to more than one person, I'll omit further personal details.
Budget: $50/day
If your idea requires significant ongoing time commitment, that is a major negative.