Plug-in cars save gas and cut pollution, but at a cost. The Nissan Leaf has a maximum driving range of about 75 miles. The Chevrolet Volt seats just four people. And at nearly $40,000 apiece, neither is cheap. The Ford C-Max Energi plug-in hybrid, by contrast, seats five and combines gas power and a grid-charged lithium-ion battery to reach the EPA-certified equivalent of 108 mpg. It goes 620 miles on a full gas tank and battery. And at $29,995 (after tax credits), it is by far the most affordable plug-in on the market. It's the kind of car that could, just maybe, take automotive electrification mainstream. Here are five reasons why.