I'm pretty sure all the lockers have been removed or sealed off. There is a shop in the international terminal that will store luggage, but their rates are not listed.

Due to security regulations, Airport lockers will be out of service until further notice.

The Airport Travel Agency is a full service travel agency located in the International Terminal Main Hall, Departures/Ticketing Level, near the security checkpoint for Boarding Area G. Services include travel reservations, travel insurance, luggage storage, overnight express delivery, Notary Public, Western Union, faxes and photocopies.

Open daily from 7:00 a.m. to 11:00 p.m.
Telephone: (650) 877-0422

http://www.flysfo.com

You might also look in the San Francisco forum here on FT.