As gas prices continue to inch closer to the 4 dollar mark on the Central Coast, you may be looking for the cheapest gas. At last report, the Arco at 1606 N. Broadway in Santa Maria was selling gas for 3.50 a gallon for regular. in San Luis Obispo, the cheapest gas was at both of the Conserv Fuel gas stations on Broad and Santa Rosa at 3.88 a gallon.