[fovc]

CO2 emissions alone add ~$0.50/gal or ~25% if you had to capture all that carbon.

[1] Can't find a great all-encompassing source, but e.g.: http://www.c2es.org/publications/cost-us-forest-based-carbon... says $30-90 per ton

[2] Burning as is about 9kg CO2 per gal. http://www.eia.gov/tools/faqs/faq.cfm?id=307&t=11