Spent a few days in SF 2yrs ago whilst working over in the States.
I Found the Carthwright Hotel very good.
Its small Hotel, very Clean, not too expensive,
Can't remember how much it costs us, but can safely say it was very good value for money.(Very Reasonably priced).
Its on the corner of Sutter and Powell just a couple of minutes walk for Chinatown, Union Square, Market Street (In other words very central).
Blues and Jazz bar not far away if your into it.
Has Car Park on next Street, around corner from Hotel, just organised at Reception when i arrived to leave the car in Carpark for 4/5 Days.
Hope this helps.