Not strictly AAR related I know, but, the M74 cost £692 million and original estimates were £445 million. Which unless i'm very much mistaken is not 3x the original estimate.
What I actually wanted to point out was using BAA's guide price, and the estimates from the Scotsman, a potential investor in EDI is going to have to fork out £800 million to purchase and upgrade the airport to cater for long haul (or heavier aircraft) at Edinburgh, and in this financial climate, I can see very few companies or consortia being willing to shell out that sort of money for an airport, which may take many a year to return on that investment.