The cost of the 49ers‘ new stadium in Santa Clara has increased by $157 million to nearly $1.2 billion, as revealed in the first of several key approvals the city made this week.

The stadium project as a whole will cost roughly $1.177 billion, in contrast with the $1.02 billion estimate presented in December, according to a complex financing deal Santa Clara leaders approved 6-1 Tuesday night.

Construction alone, estimated to cost $1.05 billion, will be the biggest expense. Building the stadium will cost $29 million more than previously projected because of several design tweaks, including reconfigured stair towers; an expanded network for cell phone service; upgrades to the heating, ventilation and air-conditioning systems; and other changes, according to the 49ers.

There’s also a new set of expenses: $50 million for emerging technology upgrades.

“This will be a cutting-edge, new-technology building because we’re in the heart of Silicon Valley,” said Larry MacNeil, the 49ers’ chief financial officer. “We believe we need a significant budget to pay for things not currently on the market.”

Finally, $78 million will be spent on interest for the construction loan, legal expenses and other costs. Construction is slated to begin this summer and finish by fall 2014.

All those details were nailed down Tuesday in a final financing plan, a final construction budget and the stadium lease.

But even though the cost of the project has gone up, the costs on the public will go down, the team says.

The city’s Stadium Authority, which will oversee stadium operations, is expected to take on less debt because fans appear to be buying seat packages faster than anticipated. If those sales don’t reach $162 million, the team will make up the difference.

MacNeil wouldn’t disclose the number of packages that have been sold, and critics say the team has not fully disclosed the financial risks involved.

“If they’re going to be using that as how they’re going to pay off a public debt, they should be saying how much they sold,” said Santa Clara resident Deborah Bress, who, as part of the grassroots group Santa Clara Plays Fair, recently led a failed legal challenge against the stadium. “That should be open-book.” The group says it may appeal a Santa Clara Superior Court judge’s rejection of a proposed referendum that would allow voters to reject the construction loan to build the stadium.

Councilwoman Jamie McLeod was the dissenting vote Tuesday. “I think it’s our responsibility to go back to the voters and ask them to make a decision on the project with all the information before them,” she said. “I think moving forward is not the appropriate step.”

Under the stadium lease, which has not changed, the 49ers will pay the city’s Stadium Authority about $30 million in annual rent.

The city’s general fund, which pays for city services, is expected to receive a base rent of $40 million over the 40-year lease and $155 million from non-NFL events hosted in the facility during the offseason, such as concerts.

Members of the Santa Clara City Council, acting as the Stadium Authority, are scheduled to meet again Thursday to consider another round of documents for the stadium, including a non-relocation agreement that would formally commit the 49ers to Santa Clara.