The BART train costs less than $ 10. That's the first transposition of the airport to San Francisco. Then, one can walk to Pier 39 which is 2 miles or use Taxi ($ 9.00) or Uber / Lyft ($ 5.00).
Taxis are always available at the taxi stand outside each of the 4 terminals of the airline at the airport, on the lower level, outside the baggage claim area.
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