We need to pay attention to this as GM and Nissan roll out their new green cars to great fanfare. The Chevy Volt, a hybrid with a lithium-ion battery, can go 35 miles on electric power alone (after charging overnight, for example), and GM brags on its website that if you limit your daily driving to that distance, you can "commute gas-free for an average of $1.50 a day." The Volt's price is listed at a very reasonable $33,000 (if you qualify for the maximum $7,500 in tax credits). The fully electric Nissan Leaf is advertized for an even more reasonable $26,000 (with qualifying tax credits, naturally). What a deal — and it's good for you, too, the carmakers want you to know. As GM helpfully points out on its website, "Electricity is a cleaner source of power."