We've split this discussion off from the old and obsolete SFO lounge thread to avoid confusion.
/Moderator
One option discussed in that thread, for showers at (then) $15, was the International Terminal Freshen Up! facility (currently closed):
Showers
Freshen Up! offers shower facilities, toiletries, ironing facilities and undergarments. Freshen Up! is temporarily closed for remodeling and will re-open on October 31, 2014.
International Terminal, PMain Hall,, Pre-Security
Hours of Operation: Daily, 7:00 a.m. to 11:00 p.m.
Phone: 650.877.0798