The firm's New York office produced the figure for the Congressional Budget Office, the US government's economic unit.
This figure, which the consultant described as "very conceptual", does not include replacing surrounding buildings or infrastructure.
Hanscomb was previously involved in costing the recovery programme after the terrorist bomb at the World Trade Centre in 1993.
The figures came as plans were announced plans to build four 60-storey buildings from the rubble of the destroyed twin towers.
Developer Larry Silverstein, who bought a 99-year lease on the centre three months ago, will leave a space for a memorial.
Silverstein said he had received hundreds of letter urging him to rebuild on the site, which contained about 10% of the office space in lower Manhattan. The towers could be completed by 2005.
New York high-rise architect Bruce Fowle backed plans for shorter towers. He said: "Instead of two huge high-rise buildings there should be a series of them that work in the context of the city."
New York aftermath
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拢8bn pricetag on new World Trade Centre
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