Intermountain Gas Co. plans to reduce its prices by a combined $14.4 million starting in October, citing strong supplies keeping its cost of natural gas down.  Thursday's proposal, which still needs to be vetted by the Idaho Public Utilities Commission, would reduce the average residential customer's yearly cost by nearly $26.00, or a little over 4 percent.  The average commercial customer's cost would fall by 7.7 percent, or $228, according to the proposal.  The company wants these price cuts to take effect on Oct. 1.  Intermountain general manager Frank Morehouse says U.S. natural gas production is at an all-time high, with companies even drilling in Idaho.  He says that supply strength is driving the lower prices.