I was looking a room near the center of SF. I couldn't find any room below $120 but then I found Leon's room. It is not that close to the center (normally it took us 40min using Muni), but the price was more accessible.
The house itself was sparkling clean and had everything that you would need. Please be aware that this house does not have a kitchen; it has a small fridge and a kettle though.
Our room was in the entrance of the house. The walls were pretty thin, so you will hear steps from the second floor and the living room (nothing anoying, but you will notice it)
Leon was a very nice and helpful, he frequently asked if we needed something and Everytime I saw him he was very polite.
You should consider this room as a solid option if you are traveling to SF!