Here's another parking tip. If you are renting a car, there is a National Car rental center 2 blocks away up on Bush St. You can rent a car one-way back to SFO airport at no extra one way charge, this location is considered a co-station with SFO. So I usually fly in, take the BART into the city and just stay on foot while in the city and then on the last day rent a one way to SFO at whatever # of days I want for the rest of the trip so there is no extra parking cost by avoiding having a car in the city.
Hertz is a couple blocks to the SE, I don't know if they will charge you extra on the one-way. A lot of times they want to get the cars back to the airport so they won't.