I stayed at The Herbert Hotel in Union Square San Francisco. It's a hotel but they also have rooms available via Airbnb. The rooms are extremely affordable at about $70 per day (pricing subject to change) considering the location. The room is dorm room style with two bunk beds that are top-bunk only without bottom beds, but there's a desk under each bed.
For a two week stay they did room service only three times. The water facet in the bathroom stays on about 2 seconds when you press down on the faucet, so you have to constantly hold it on with one hand... or just use the tub to shave!
The hotel is quiet (minus the pigeons that camped out on our window sill) and safe. Location is excellent as the Powell Street BART & MUNI station is a block away for easy access around the Bay. There's also a 24/7 Walgreens two doors down if you need to stock up your minifridge in your room with water, beer, etc.
It's a bit of a pain constantly climbing up the ladder to the top of the bed, and I wish the room had a small couch or something, but the price is excellent given the location. If you want five stars expect to pay an arm and a leg. Anything else this cheap means shared room and/or shared bathroom. This was a private room and private bathroom. They also didn't charge for a second person to stay in the room. Someone works at the front desk at all hours and the front door to the hotel is locked for security reasons after 7pm (access via your room key or the front desk employee will buzz you in).