From the DOE's Energy Information Agency's Voluntary Report of Greenhouse Gases Program, I was surprised to learn that a gallon of motor gasoline generates almost 20 pounds of CO2. That sounds like a lot. But ...
If I drive my car 10,000 miles per year and get 25 miles per gallon, then I generate about 8000 pounds (i.e., 4 tons) of CO2 per year. If I was a RGGI member, I would need to spend $12.28 to purchase 4 permits for a ton of CO2 at a price of $3.07 per ton in order to continue to drive. And I thought my $40 TerraPass offset was cheap.
Note: Corrections to sloppy math/conclusions welcome!