Back in '03 I drove an auto 92 accord from (near) Burlington VT to southern CT on.... no lie, $10 of gas, which would be about 6 gallons. It was 260 miles, so that's 43mpg. I averaged 75mph too.
I had filled my tank when I left, then when I got home to CT I filled it again and the pump shut off at $10. crazy. Maybe the pump was off, or maybe it was the overall decrease in elevation. I don't remember any wind.