Building the Miami Marlins’ new stadium may end up costing tens of millions of dollars less than planned.

And where would the left-over money go? To a maintenance reserve that would save the Marlins from having to dip into their pockets in the future to maintain and repair the stadium.

Part of the deal the baseball team negotiated with Miami-Dade allows the Marlins to keep all construction savings, and apply the money to future maintenance and improvement costs at the ballpark. Because the Marlins are responsible for a big chunk of those expenses anyway, the lower construction costs could mean a windfall for a team that is cutting player payroll and facing continued backlash over public dollars poured into the county-owned stadium.

As of the end of December, the team had spent only about $102 million of the $131 million it had agreed to kick toward construction.

Stadium construction was budgeted at $515 million, with the team benefiting from any savings from the total cost if the ballpark came in under budget.

“So they’re able to simply roll this into a fund that they would otherwise have had to spend money on,” said author Neil DeMause, whose 2002 book Field of Schemes skewers the greed of wealthy ballclub owners and explains how politicians bow to the pressure of handing over public money. “That’s interesting.”

A look around at some of the newer ballparks in the league shows the Marlins are likely to spend tens of millions more over the first decade upgrading the Little Havana ballpark than the $1.75 million a year the team, the county, and the city of Miami are obligated to place in the capital reserve fund each year. The stadium agreement stipulates the Marlins and the county each place $750,000 each year, and Miami $250,000, in the reserve. Any expenses over the $1.75 million in any year would have to be paid by the Marlins.

Elevators and escalators will need repair. Concession stations will have to be updated. Lights will have to be replaced. The typical lifespan of a new electronic scoreboard is only seven years, with a cost well in excess of $10 million

The Seattle Mariners’ Safeco Field has undergone more than $80 million in upgrades since 2000, including a new $11 million scoreboard built last year, with the entire cost picked up by the ballclub.

Stadium improvement costs were almost the same for Milwaukee’s Miller Park, though the team wasn’t on the hook for nearly as much money as the Mariners. That’s because the public/private partnership between the team and the Milwaukee Ballpark District makes the district the landlord and 70 percent owner of the franchise. Renovations must be approved by the authority unless the Brewers want to pay for them with their own money.

Each year the Brewers place $750,000 a year in an improvement reserve, while the authority invests $1.75 million. So far, Miller Park District Executive Director Mike Duckett says his authority has spent about $20 million, and he believes the Brewers have spent about twice that amount.

“If we go over, it stipulates the district must cover the cost,” said Duckett. “But we meet with the Brewers each year asking what their needs are. It’s worked out pretty well so far. I think we still have about $9 million in the fund.”

Like most of the Marlins stadium deal, the capital improvement clause heavily favors the team. The total $642 million for ballpark and parking facility agreement cost the county $384 million, the Marlins $131 million, and the city $127 million, mostly for the stadium’s six garages. Yet the Marlins collect almost 100 percent of the revenue, including those coming from concessions, concerts and parking fees.