In simplest terms, staying home.
California, and especially the San Francisco Bay Area, are replete with nice clean sandy beaches. Anything within a couple hours of your house makes lodgings effectively free, and nullifies the need for airfare.
With the money saved, you can fill in a lot of the "key remembrances" of a more exotic destination by significantly upping your dining destinations, incorporating a spa visit or three, and/or chartering transport to take you from place to place on your "staycation".
Also, being able to take a few days off, break your routine, and see your city as an outsider, or at least with somewhat fresh eyes, can be invaluable to feeling greater satisfaction and connection with where you live and work. In a sense, it's a vacation you can rave about at work, that any of your coworkers can do themselves!
What are the cheapest beach destinations for vacations, taking into account both lodging and airfare from California?