Affordable energy prices are brightening Leonore Barfield’s winter. Gasoline has dropped about 50 cents a gallon from last year near her home in the 6,000-person town of Raton, N.M.—lowering the cost of trips to restaurants, movie theaters or the closest Walmart, in neighboring Colorado. And even though cold weather has blanketed the area since October, falling natural-gas prices have helped the 63-year old retiree keep her three-bedroom home comfortably warm. …