Union Square

Yes you can see San Francisco on a budget.  And you don't need a car to do it.  Between BART (the subway), MUNI (the bus system) and the cable cars, you can get everywhere and not deal with parking (always a pain in this city).  Parking fees are high and parking places are hard to find.  So leave your car at home, stay in a cheap hotel and spend your money on what really matters - getting to see and do everything you've always wanted.