For me bike commuting started out as something to do for fun and make me feel better about not ever going to the gym. I also still have my car because I commute about 50%, and as a result I've probably spent more bike commuting than I would have if I just kept driving 100% of the time. If I factor in not paying for a gym membership that helps, but my current employer for the last 10 years has a free on-site gym so that isn't even a factor any more. Not complaining, there are lots of things I could be doing that are worse for my health and my wallet.