I think its safe to say that what Lord Foster (I think thats his name) has pitched is a very ambitious idea.
The HS train that will run from the airport will also cost a fortune to travel on. As most of you are probably aware, the Gatwick Express costs a huge amount of money to travel on, and the journey is still quite long. The London Underground connection at Heathrow means people can travel to London for a much cheaper fare (although its still not so cheap).