Statewide – The cost of gas is staying down for now, with the average price well under $4. Gas prices in Indiana have fallen 22 cents in the last week. That makes the average cost for gas 77 cents cheaper than this time last month. Right now, gas in Indiana costs around $3.41 a gallon. In Terre Haute, the gas average is $3.20. Over in Illinois, the state’s average stands at $3.60.