For 24 hours, I would just hang on to the car rather than go through the bother of returning it and using a taxi in and out of SF. Even the most expensive hotel parking will be no more than about $40 for the night. Taxi fare both ways will be in the $90 range. Taking Bart will cut the cost of dropping the car to about $10 per person, but even if I were doing this alone, I don't think the hassle would be worth the $30 I would save by avoiding the parking charge.