Mayor Bill de Blasio on Monday said he’ll revisit instituting a tourist fare for the Staten Island Ferry, which could bring an estimated $2.4 million in revenue annually for the city.

The mayor has eyed the idea before, but his administration warned that implementing the fare could present challenges, de Blasio said in Brooklyn.

“Of course I’m open to it,” de Blasio said. “If we can figure out a way to do it, I’d certainly prefer to have the revenue while making sure that nothing we do changes the sanctity of it being for free for New Yorkers. So I will ask [the city’s Office of Management and Budget] in particular to look into it and see if something’s changed and if there is a way we can actually reach that.”

Charging tourists $4 to ride the ferry could generate roughly $2.4 million annually, according to an analysis from the city’s Independent Budget Office in 2014. That revenue estimate is based on a fare that exempted only Staten Island residents and other city residents who work in the borough.

The estimate also accounts for the costs of installing and maintaining such a fare collection system over a 15-year period. Purchasing and installing the equipment needed to collect fares — ticket vending machines and gates — would cost $5.1 million. And operating the system would cost another several million each year.

Although the IBO expects the city to net an average of $2.4 million each year from the fare, the analysis highlights how many questions its implementation would pose.

“The answer I’ve gotten when I’ve raised [the fare] to the folks in different agencies is that it’s not as easy to do as one would think — and that’s a real factor,” de Blasio said. “If something is too cumbersome or if it comes with other costs, it may not be as worth it as common sense would make you think.”