Agree TShirt - $2.50 takes into account production costs, piping, risk, NPV projection reduction - I base my US gas values on about that and then discount a further 50% as I would want at least a 2-bagger average on my investments.
Note Gas is much cheaper in Aust and production more expensive and I only allow $0.80 on gas finds in Aust. Fortunately Oil is approximately the same price everywhere.