Do you know of an example of paid reviews? This would seem like a big conflict of interest and I have not heard of any but predatory journals doing that.

Historically, a large cost was typesetting and print publication. However, print is used less and less in favor of online subscriptions and typesetting is mostly using the publisher's LaTeX style file.

The "value" provided by journals seems to be:

- communication with the editor (unpaid, mostly senior peer researcher)

- review (unpaid peer)

- software to manage submissions, reviews etc (commercial)

- proofreading for typos and some fine tuning for figures and layout (useful)

- prestige of having published in an important journal (very valuable for your career)