Here in San Diego Costco gas is only a couple of pennies cheaper than some of the Arcos and Exons!
http://www.sandiegogasprices.com/index.aspx?&area=San%20Diego%20-%20Central&area=San%20Diego%20-%20East&area=San%20Diego%20-%20NE&area=San%20Diego%20-%20North&area=San%20Diego%20-%20NW&area=San%20Diego%20-%20SE&area=San%20Diego%20-%20South&area=San%20Diego%20-%20West
The Navy base is (military only with ID) is $4.32 in San Diego