From what I hear the Americans speaking about often, I believe it is even cheap in San Francisco.

Depends on when we're talking about. If you asked 2 years ago, yes that was about normal. However, this last year, for downtown SF, it's expensive. You can find a private room downtown for about half that[0] if you sign a year lease.

For a short term stay, it's about on par w/ the price of an airbnb uptown.

[0] https://www.urbanests.com/

That's not unreasonable for a house with a few roommates in SF. A studio in the same neighborhood would be maybe $2k or a bit more, and a small, kinda-crappy 1-bedroom would start at $2.6k.