It could cost as much as $77.3 million to expand the state's largest airport for a Denver-based carrier.
Denver International Airport had estimated the cost of expanding Concourse A at $42.5 million, with undisclosed costs for a second phase of construction.
But DIA spokesman Steve Snyder says the new figure represents the maximum cost of the project through completion in October 2005.
The original estimate didn't include the cost of optional gates.
The total cost will depend on how many gates Frontier Airlines wants. The airline must make a decision by spring.
Frontier and the city agreed on the expansion last month as part of a three-way deal with United Airlines valued at $137 million.