Bagso, I'm not sure if your comment is aimed at me, but please don't shoot the messenger.
I strongly support MAN, but I just don't buy the idea that supporting MAN necessarily means opposing LHR. I don't think it helps our industry for one airport to be fighting another.
That being said, I do agree with Shed that the cost of R3 is ridiculous. I have my own ideas why this is the case, but I won't bore others with them. I also agree that public money should not be used to develop R3 - my argument is that I don't think this is going to happen. I may be wrong in this, in which case I would join you and Shed in opposition. Based on the pretty detailed analysis by Davies, it does appear that R3 will wash its face, even at the ludicrous cost estimate that is being proposed (and including the Davies estimate of surface access costs).
However, I would advise against latching onto the TFL arguments about even higher costs. Their basic argument is that road congestion in the Heathrow area will continue to be very bad, such that (a) you shouldn't worsen it by further developing LHR, or that (b) if LHR is further developed then the road problems need to be solved by throwing vast sums of money at them. The problem here is the usual "sauce for the goose/sauce for the gander" issue. MAN would be ill-advised to go down this route in opposing R3 as it could easily find its own future growth being restricted because of concerns about congestion on the M56 and parts of the M60. Just be careful what you wish for.
There are no easy answers to any of this, but my greatest fear is that by opposing R3, MAN and other airports will suffer longer term adverse consequences. All airports need to work together to fight the forces that seek to restrict the growth of air traffic in our country.
(Ps sorry for the essay)