The price of mailing a letter will fall for the first time in nearly a century this Sunday. And the U.S. Postal Service, which was ordered to cut the price by its regulator, is not happy about that. USPS said the decline in the cost of a postage stamp, from 49¢ to 47¢, will cost it $2 billion this year, and make it more difficult for it to compete and provide the service its customers demand. […] The Postal Regulatory Commission, the independent government agency which oversees the USPS and its pricing, acknowledges the Postal Service will lose $2 billion...