Airports group BAA has said a second runway and new facilities at London's Stansted airport will cost £2.7bn ($4.71bn) to construct.
BAA wants to boost passenger capacity at Stansted airport
The figure is close to one-third below previous government projections.
BAA hopes the runway, which is strongly opposed by local residents and environmental groups, will boost the UK economy and be ready by 2013.
Separately, BAA said 10.4 million passengers passed through its airports in November, up 2.2% on a year ago.
BAA operates airports at Heathrow, Gatwick and Stansted in London, and Southampton, Edinburgh, Glasgow and Aberdeen.
Mike Clasper, BAA chief executive, said: "'We've worked very hard in the last two years to ensure that Stansted G2 [runway two] will deliver great value to the UK economy, to our airlines and to people using the airport.
"We've also examined in great detail the environmental impacts of the project, in order to ensure that they are reduced as far as possible."
The plans for Stansted - which would more than double the airport's yearly passenger capacity to 50 million - are opposed by some airlines, which fear higher airport charges.
Ryanair and Easyjet, which account for about 90% of Stansted's business, are worried they will effectively have to fund the expansion.
New British Airways boss Willie Walsh has also questioned the need for a new runway at Stansted, and promised to fight any resultant increase in airport charges to pay for it.
And the Stop Stansted Expansion Group said the BAA proposal would cause catastrophic damage to the environment.
Campaign director Carol Barbone said: "A second runway in any position would be an environmental catastrophe for which there is absolutely no economic justification."