The average price of regular gasoline in the U.S. has dropped six cents in the last two weeks, according to the Lundberg survey. A gallon of regular gas now costs $3.52 on average. In Arizona, Gas Buddy reports the average price has dropped from $3.70 to $3.35. San Francisco has the highest price at $4.01 per gallon. Charleston, South Carolina, has the lowest at $3.14 per gallon. And the average price in California is $3.97 per gallon, which is up 16 cents from two weeks ago.