Prices are coming down because airlines are now saving billions of dollars thanks to lower fuel prices and because more seats have been crammed into planes, spreading out costs over more passengers. The generally good news about fares comes in a report released Monday by the Airlines Reporting Corp., which processes ticket transactions for airlines and travel agencies such as Expedia, American Express and Carlson Wagonlit. Travelers can thank lower oil prices and more seats on planes for keeping this summer's airfare in check. Airlines at the start of the year paid $2.13 for each gallon of jet fuel, down 30 percent from last year's $3.03, according to the Bureau of Transportation Statistics. With U.S.