Try parking at a hotel or motel where long term parking is available and have free shuttle to cruise terminal
We used the long term at the airport (15 day cruise), took the train to downtown and a uber taxi from the terminal to the Embarcadero. The train is very very affordable and faster than a Uber, the uber fare is just a couple miles and the parking lot is very unexpensive and secure.
There are 2-3 lots on the Embarcadero that provide parking for families going on cruises. I don't know the pricing since we took a shuttle to the terminal fro San Jose. Have fun!
Lot of places in SFO offers cheap long-term parking, you can Google and call them for details
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