The best pricing can be found in the month of April. Prices to Helena from Chicago-O'Hare Intl average $334. You can even find prices in April for less than $334, as users have found deals to Helena from as low as $121. The month of December appears to be one of the more expensive times to travel to Helena from Chicago-O'Hare Intl. Flying in the targeted month can save you up to 67%.