Mayor Bill de Blasio should include public support for a five-borough Citi Bike expansion in his next city budget, City Council members said Wednesday.

But just how much it would cost taxpayers is unclear.

“We know the value that this great service brings to New Yorkers and we want to see it spread further so that more people hop on these bikes to get around,” said Manhattan Councilman Ydanis Rodriguez, chair of the Transportation Committee, in front of City Hall’s steps.

“Unfortunately, without city funding this year’s budget, Citi Bike’s plan for expansion will come to a screeching halt.”

A majority of Council members, 34 in total, support the move to buoy the bike share with taxpayer money in order to bring the service to the likes of the Bronx, Staten Island and other less densely populated areas of the city where Citi Bike might otherwise be difficult to succeed under its current, privately-funded model. Most cities around the country already pump public money into bike share systems.

“I don’t think I’ve ever seen 34 of us get together and push for a budget allocation like this,” said Manhattan Councilman Mark Levine, who called the rally a “testament” to the demand for a “reasonable, sensible investment into Citi Bike.”

Levine was one of several supportive lawmakers on hand who have recently seen the service begin to expand into their district with pleasing results. And they were not alone. Seventy-one percent of New Yorkers in a newly published poll said they either “strongly support” (42%) or “somewhat support” (29%) “expanding Citi Bike to more neighborhoods in all five boroughs.”

The poll, which surveyed 880 likely city voters, was conducted by Penn Schoen Berland Research and commissioned by Transportation Alternatives, an advocate for the expansion.

Motivate, Citi Bike’s operators, is currently having conversations with the administration to shape out what a five-borough expansion would look like. Without a plan established, operational costs are difficult to estimate, according to sources familiar with the matter.

Citi Bike would likely have to expand from a planned fleet of about 12,000 bikes by year’s end to about 70,000 or 80,000, according to rough estimates from Polly Trottenberg, the commissioner of the city’s Department of Transportation, at a recent Council hearing. Currently, the installation of about 2,000 bikes requires a capital cost of $12 million, according to Motivate.

“The mayor has said he’d like to make Citi Bike a five-borough system and we’re in active conversations with Motivate on how to continue to strengthen this popular program that the de Blasio administration rescued from the brink of collapse, put on solid footing, and will continue to expand to more neighborhoods this year,” said Austin Finan, a mayoral spokesman, in a statement.