United and ANA have a few bargain flights via:
https://mobile.united.c
http://www.ana.co.jp/asw/wws/us/e/
Sample Dates:
7 January 2018
22 March 2018
$400 flying with United
$416 flying with ANA
Might I recommend you fly ANA for a few bucks more with layover in NRT, rather than SFO with United.