The operating budget for the Olympics and Paralympic Games in 2016 has jumped 27 percent to seven billion Brazilian reals ($2.93 billion).
Officials told a news conference on Thursday the new total for the combined Games in Rio was less than London spent in 2012, explaining the rise was due to factors like inflation and new technology.
Four sports have been added since the bid was won in 2009 - rugby sevens, golf, paracanoe and paratriathlon - and the revised bill also has more detail.
"Our goal is to hold a magnificent Games. We want to ensure a balanced budget (and) avoid any transfer of public funds to the committee," said Artur Nuzman, president of the Brazilian Olympic Committee and the local organising team.
Just over half the budget will come from local sponsors while the International Olympic Committee (IOC) will contribute 21 percent.
Around 13 percent is to be raised by ticket sales, nine percent from international sponsors and six percent by licensing and other income.
A quarter of the budget was originally supposed to come from government sources but officials said they would no longer take public money.
That decision comes seven months after the biggest public protests in 20 years erupted on the eve of the Confederations Cup soccer tournament, the test event for the World Cup that will be held in Brazil in June and July this year.
Hundreds of thousands took to the streets angry at what they perceived as public funding for grandiose football stadiums while schools, hospitals and public transport were in a state of disrepair.
"I think it's a huge risk saying seven billion reals," a source with direct knowledge of the budget told Reuters.
"We should put it much higher, to around 10 billion, so we have some breathing room and a chance of having some cash left over at the end."
The budget does not include venues, infrastructure or security.
The government will announce the bill for venues and other projects on Tuesday and the cost of infrastructure such as new metro lines and bus lanes will be revealed in March, even though some of the schemes have already begun.
One of the main selling points used by Rio was that an Olympic Games would help the city modernise and resolve some of its chronic public transportation deficiencies.
Nevertheless, the self-appointed 'Marvellous City' is already facing criticism.
The tender to build the Deodoro complex where 11 events will be held is still to be opened and the picturesque bay where sailing events will be staged is massively polluted.
The stadium where the athletics is due to take place was closed down last year after engineers warned the roof could blow off in high winds. It is scheduled to reopen in November.
IOC inspectors who visited last year warned that unless the pace of construction picked up soon, some arenas may not be ready in time to host test events ahead of the Games.
However, IOC president Thomas Bach set an upbeat tone earlier this week.
"After hearing the President's strong commitment to the success of the Games I am even more confident than before we will have an exciting and brilliant Olympic Games," he said.