Just returned from a 6 day trip from Chicago area to Hailey Idaho and back. Only run 87 Octane (not the 85 Octane that some western states sell).
Iowa City Area 8/30/17 $2.349 per gallon
Cozad, NE along I-80 8/31/2017 $2.399 per gallon
Rawlins, WY along I-80 8/31/2017 $2.869 per gallon
Arco, ID along US 20 9/1/2017 $2.879 per gallon
Columbus, MT along I-90 9/2/2017 $2.49 per gallon
Oacoma, SD along I-90 9/3/2017 $2.699 per gallon
Poynette, WI along I-39/90/94 9/3/2017 $2.659 per gallon
It seems as if the price of gas has risen somewhat during my trip. I was especially surprised at the prices of gas in Wyoming and Idaho. Not sure if the gas taxes are higher in these states or not, but the prices in these states were significantly higher than elsewhere.