The Big Apple estimates having to spend about $20 million to fight the spread of coronavirus, New York City’s budget czar said Monday.

Melanie Hartzog, director of the Mayor’s Office of Management and Budget, said during a City Council hearing that the city had already spent $3.8 million combating the disease and expects it will ultimately need to spend at least $20 million — the same amount spent to tackle the Ebola crisis nearly six years ago.

“We do have a plan,” said Hartzog, while testifying on Mayor Bill de Blasio’s proposed $95.3 billion budget for next fiscal year. “I think the proxy for these efforts is … looking at Ebola, where we spent about $20 million. I think that’s good proxy for us.”

Hartzog insisted de Blasio “has made this a top priority,” adding that city agencies “should be spending and [already] are.”

Neither the Mayor’s Office nor the Department of Health could account for how the city already spent $3.8 million on coronavirus prevention when asked by The Post.

Gov. Andrew Cuomo announced plans Wednesday to have the state set aside $40 million to combat coronavirus, and Hartzog said the city has already requested “half of it” to reimburse its expected costs.

She also said the city is reviewing whether the coronavirus could hurt tourism and other parts of the local economy.

“We are most certainly concerned about that, given the volatility of the market and its potential impact on tourism,” she said.

A 39-year-old Manhattan woman on Sunday become the first person to test positive for coronavirus in New York City after returning from Iran with her husband. Her husband also is under self-quarantine and is being tested.