New York Times:  “opting for models that promise better mileage through new technologies does not necessarily save money, according to data compiled for The New York Times . . . . the added cost of the fuel-efficient technologies is so high that it would take the average driver many years — in some cases more than a decade — to save money over comparable new models with conventional internal-combustion engines. . . . The Volt, which cost nearly $40,000 before a $7,500 federal tax credit, could take up to 27 years to pay off