I’m aware, from doing Part1 in person, that some used student accommodation to say in SF. For example, http://www.usastudentresidences.com offer both private and shared rooms and their 2018 rates, when I enquired in early October 2018, were;
USA Student Residences
711 Post St
Room Type Monthly
Private Room/ Private Bath $1,975
Private Room/ Shared Bath $1,700
Shared Room/ Private Bath $1,275
Shared Room/ Shared Bath $1,000
When I enquired, the private rooms with private bath were all booked up, so I think it’s best to plan well ahead.
Others I knew who stayed in SF either lived there, or knew someone they could stay with. I did search for a good value accommodation in SF, but I found that it can take just as long, or longer, to take public transport across the city as it does to arrive into Embarcadero from the East Bay.
I found that AirBnb prices dropped dramatically if I travelled 30-55mins by BART. I found the BART system brilliant, and a very easy way to get to Howard St. when you get off at Embarcadero. I stayed in various AirBnbs (e.g. Pittsburgh/BayPoint (c.53mins direct to/from Embarcadero), South Hayward (c.36mins away direct) and Lafayette (c.31mins direct trains). Of these, Lafayette was the most pleasant area by far, but also the most expensive of the three. I can give you more info if you want to DM me, although I’m aware there are many places to stay, and my experience is just one small slice of what’s available.
I can understand why you want to stay in SF, and I hope you find something good.