The expensive gear is more of a choice than a necessity. I like the cycling gear as much as anyone and I'm a sucker for whatever will make it easier or more comfortable or more interesting, but I can and often do commute with nothing more than the bike and whatever athletic clothes I'd have had anyway. Other than consumables like chains, tires and cassettes, chain oil, the expenses basically end wherever you want them to.

OP you're dead on right about the reasons "peaceful, easy, not stressed out. ... wide awake and in a good mood..." and I'd just add "fun". My driving colleagues have such a hard time accepting these as real reasons, that I think of them as our "secret" which you're now in on.