https://brownstone.live/ has several buildings with "capsule housing" (pods) for about $800 per month. there may be similar places. there may be hostels too.
be careful with AirBnB etc., some places may be very cheap, but they may be in bad neighborhoods. some areas of SF have lots of homeless on the sidewalks, plus street crime. if you find a place, ask here about the neighborhood before you sign up.