Cost is a subjective subject. Recently, Vermont Gas released a study they claim shows the "life cycle" analysis of "natural" gas really is a cleaner alternative than coal and oil, so we should build the Addison Natural Gas Pipeline and start saving greenhouse gas (GHG) emissions along with a bunch of money from having a cheaper fuel source. They hired a consultant company to do their study and they produced an inch-thick volume of tables and graphs supporting their claims.
Gas companies claim that "natural" gas burns cleaner than oil or coal so it's better for the environment and the opponents say that if you figure in all the "fugitive" methane that is produced during the extraction, refinement and distribution (life cycle) of "natural" gas, the end result is worse than the other two fuels. There are lots of other factors to plug into these spreadsheets and cost analyses, but GHG emissions is the "evil du jour" right now.