A very good post from Shed. Yes both LHR and LGW are stonkingly expensive.
Anyone interested in the content of the projects should look at the Jacobs/Leigh Fisher reports on the Commission website.
I don't know the content of Manchester runway 2 project but my reading of the LHR North-West option is that the runway plus taxiways component of the work is of the order of £1bn before allowing for risk. So it might be a few times the price probably for a bigger and more complex project. But that's not really the point.I think the key issue is more the sheer size of the M25 costs, the land acquisition, the T6 costs and the new sections of railway to deliver the project in its entirety which take the project from £1bn to £12.9bn before risk and optimism bias which add another £5bn or so.