Think like someone who lived in the Haight (Ashbury district) in the late 60s. They must have subsisted on little--cheese, crackers, beer, wine, nuts, fruit. The beauty of San Francisco is that neighborhoods such as these have barely changed in decades. So pretend you are local and head into a market in the Haight and pick up a baguette and cheese lunch.
Enjoy the outdoors. This means the Marina District, or more pointedly, the Marina Green (see picture) where you can jog, walk, workout on equipment at the park or simply gaze out at the bay (including the Golden Gate Bridge to the west, and Alcatraz straight ahead). Also, don't miss the parks in San Francisco. Near the Haight you'll find the easternmost tip of Golden Gate Park. Other great parks in San Francisco include Dolores (in the Mission District) and Buena Vista Park (in the Haight).
Time your activities toward the cheaper option.For example, if you go to the movies after midnight, you can sometimes find a cheap deal. Or come into a bakery at the end of the day and you'll be able to buy muffins half off.
Walk all over. San Francisco is, in part, special because of its unique geography. The topography of hills is horrific for the driver--especially those unaccustomed to the land--but truly breathtaking for the pedestrian. Walk around the Presidio to a rest stop that overlooks the entire city. From this vista you will see the San Francisco Bay, Alcatraz and in the foreground, the Palace of Fine Arts.
Sleep at lower-cost options such as a youth hostel in the city, or a hotel/motel just outside San Francisco. Because of BART (Bay Area Rapid Transit), San Francisco is easily acessible from many other towns in the "Bay Area."
Venture outside the city. Sausalito (seen here, looking towards San Francisco) is expensive, if you don't play your cards right. You want to head to Molly Stone's for some great picnic fixings, then tour the area around the boat docks. If the weather's nice, sit on a bench and spend aboslutely nothing watching seagulls pass by.
