Doug Proctor points me to this article about the economics of shale gas. Considering it is on a website called Smartplanet, it's argued in a pretty sane and sensible manner, concluding that $2/mcf is a function of oversupply rather than the true cost of shale gas.
I don't have a problem with this argument actually. Figures in the range of $5-7/mcf are often quoted for the range in which fracking operations become economic, perhaps more outside the US where the shales are more readily exploited than in the UK. This would still be much cheaper than the kinds of prices we pay for gas now and there are energy security considerations in favour of shale too.
But at the end of the day, the economics of shale are not relevant to the government's decision about whether to let fracking commence. Arguments over what is cost effective and what is not are just so much hot air. We have markets to settle the bickering.
(Of course, it goes without saying that the energy market is so rigged and distorted by subsidies, obligations, surcharges and price floors that it is impossible for it to function properly, but that's another argument).