If you need to stay in San Fransisco, the hostel near the Presidio is excellent.
I highly suggest a turkey sandwich at Arguello Market. Fairly close to the hostel and bridge.
The hostel at Monterra is very good. The breakfast at the Half Moon Bay Airport is awesome.
This is the view from my room.
If you want a hostel room be sure to book WELL in advance.
There are a few warmshowers hosts in Santa Cruz.
Why just Santa Cruz? Things don't really get good to Big Sur. You should at the very least try to make Monterrey. You will pass through Elkhorn Slough, there is an excellent Mexican restaurant in town that makes the best burrito I have ever tasted.