“Given that New York has so many inaccessible stations, the M.T.A. must figure out how to bring down the costs of individual projects,” said Colin Wright, a senior associate at TransitCenter, an advocacy group.

Each project can require adding two or three elevators — one to take riders to the mezzanine level where they pay the fare and one each for the platforms heading in opposite directions. Officials also frequently have to build new staircases, move utilities like gas and water lines and pay for real estate at the street level for the elevator.

“The elevator installation is really only 20 percent of the overall cost,” Janno Lieber, the authority’s head of capital construction, said in an intervie w.

Still, subway leaders have said they want to bring down the costs and are looking to other cities for lessons. The cost of building elevators at train stations can vary widely — one project in the Boston area cost about $36 million and included three new elevators and two escalators. A new station in Chicago with four elevators cost $75 million.

In New York, a developer in Lower Manhattan agreed to build two subway elevators, at a cost of about $10 million each, in exchange for being given permission to build a larger building.

Over the years, elected officials and transit leaders have repeatedly thwarted attempts to build subway elevators. Richard Ravitch, the former M.T.A. chairman credited with turning around the subway in the 1980s, fought a push to add elevators, arguing that the costs would be “enormous and the benefits illusory.”