If you're lucky enough to work close to a BART stop, you're going to save yourself about $1000/month.
Rent a room in a house close to any BART station. Berkeley is nice and cheap (it's all relative), as is the peninsula Redwood City and up, until you get to SF. The peninsula isn't actually connected to BART, it only runs south to Millbrae. You can, however, use Caltrain, which runs from san jose to sf, with BART connections in Millbrae.
The Bay Area's public transit is pretty bad, but if you're lucky enough to live and work near BART or Caltrain, you'll be fine and it'll actually work quite well.
Great tips for affordable, sane living:
-Use BART/Caltrain whenever possible
-Know Caltrains somewhat limited schedule (dont get stuck in Millbrae at 9pm)
-GO TO THE FARMER'S MARKET. The food is a bit more expensive, but is lightyears above local markets (Safeway, etc) in quality.
--The Bay is very close to one of the world's largest and best agricultural systems, and the only way to benefit from that relationship is the Farmer's Market. Safeway's food is nasty in comparison. Every town has a market at least once a week.
--And it's not just produce. They have a lot of local meats, eggs, and restaurant booths too. All sorts of great stuff. It is marginally more expensive, but just do yourself a favor and buy a tomato when they are in season and compare to Safeway. Yes, they are $1/lb more, but, it doesn't matter and you'll see why.
-Use Yelp to find good cheap restaurants. If you like ethnic food (asian, indian, etc) you'll eat for cheap and love every second of it. There is never, ever, a reason to eat at place like the Olive Garden or Chevy's. EVER. EVVVERRRR. Between the Farmer's Market and cheap foreign food, you'll eat food better than almost anywhere in the US.