As of April 2021, PLOS One charges a publication fee of $1,745 to publish an article.

I mean, seriously, I would like to publish to one of these, but who has the money to do that?

There are many other open-access journals, for example these: https://freejournals.org/. But yes, open-access is the way.

Another one, Frontiers:

https://www.frontiersin.org/

I have a stupid question but what are the costs of a journal like this? I mean, if they don't pay the researchers and the reviewers, what do they do?