I was astonished that the owner pays 100 dollars a little for hosting

Advertisement, paywall, donations, sell stuff.

Given that the asker is against paywalls (props to him!), and donations would feel weird in a site shown on his CV, that leaves advertisements and selling stuff. Or both.

A commenter mentioned “Affiliate link for rogaine and/or books about how to look good bald.”; it sounds good, as long as there’s no data vulturing. It isn’t even necessary, given that the site targets a specific demographic that is clearly related to both things. (I don’t like ads but you gotta do what you gotta do, right.)