SAN-SFO-JFK-LAX-SAN out 12/12 return 12/13, $328, 6061 miles with 500 mile minimum.
https://www.google.com/flights/#sear..._ALLIANCE;eo=e

SAN-LAX-JFK-SFO-SAN day trip 12/6 is $366.

If you want to go for an overnight trip to PHL or EWR, you can find it for between $350 and $400, but most likely you need to route through SFO in both directions to get enough miles. Here's one for PHL, out 12/12, return 12/14, $354, just barely enough miles with 500 mile minimum -
https://www.google.com/flights/#sear...-SFOSAN0UA1275