so average person takes 20K breaths a day, that's $1000/day every day for no effort.
Steps obviously vary a lot more. If you get the recommended minimum of 10K steps a day then that's $2.5K/day.
I feel like were I given this sort of earning potential I would probably seek to get in shape as a first step, which would make the step choice the overall better choice.
But breathing is a prerequisite of living, so while you may not be able to walk every day you are alive (you become disabled or elderly) you will always breath. Over the course of a life, breathing is likely the better income.
The steps option has a way higher ceiling and can give you significantly more money when you need it most (i.e. early in this scenario). The breathing one will probably net you more money in the end, but that would likely be when you already have a huge excess and it doesn't matter much.
If you walk 10k on avg a day from 30 to 70, you'd have to live until 130 to break even. It only gets worse if we consider steps walked since birth.
That's before you consider that I'd rather have money while I can walk. Even looking purely at it from a most money at the end perspective I could invest the excess 1.5k a day and make far far more than you could breathing. I could also quite likely beat 10k steps on most days, when I go to a festival or other walking activity (which I would do a lot more with all the free time I'd have) I pretty often break 25k steps.
So the expected value is much higher for walking even factoring in the chance of a horrific accident.
Of course maybe you'd rather not feel obligated to walk every day, or maybe you'd rather play it safe with breathing. Those are both valid choices, 1k/day is still more money than anyone needs. But walking definitely makes you more money by the end, and personally I'd appreciate the incentive to stay active.
That's a good point. Op doesn't state how much air intake a breath takes. Say you breath in tiny amounts of air really fast. It would be much faster to ear that money.