Get Gas for Less Than $2.40 in Sioux Falls, Prices Coming Down Gas prices have been creeping higher and higher over the last few months. Finally the prices are getting lower, depending on where you go. The average price for a gallon of gas in Sioux Falls according to AAA is $2.78. That's down a penny over a week ago but still a penny higher than it was a month ago. But one year ago, while we were in the midst of our at home quarantine, regular unleaded was only $1.81 per gallon. But it didn't matter, we weren't hardly driving at all.