As for accommodations in San Francisco, consider the Hostel at Fort Mason. Best buy in town, less than $30.00 a night with breakfast included. You might be able to grab a private room, if you're lucky (less than $90.00 a night). Fantastic views of the Bay and the Golden Gate. Reserve online or call; they're open 24 hours a day. Cook your own meals in the huge kitchen (Safeway Supermarket five minutes walk). But then who wants to cook with all the great restaurants nearby! I've been staying there for 11 years in a row.
Definitely check out the Redwoods Nat. Park on your way south. If you have the time, take the cutoff from Highway 101 to coastal Rt. 1. No doubt it will be foggy, but a wonderful drive, full of twists and turns all the way to SF. Mt. Tamalpais, just north of the Bridge on Rt. 1, can yield lots of great shots, even when it's totally socked in. And you might get lucky and nab the classic view of the Golden Gate Bridge superstructure peeping out of the fog at sunset (Drive to one of the upper parking areas on Conzelman Rd., first exit off the Bridge).
The Bay Area can keep you busy for weeks!