Trump had previously estimated the cost at US$400 million and repeatedly insisted that private donors – including himself – would foot the bill for the new building, a centrepiece of his drive to put his stamp on the US capital.
The newspaper cited a copy of a detailed cost estimate prepared for the Trump administration by Clark Construction, the contractor hired to build the ballroom.
The project began last year when Trump, with little warning and without consulting Congress, tore down the entire historic East Wing of the White House.
The White House insisted in a statement to news agencies on Tuesday that Trump and the donors were bearing most of the cost.
“President Trump and generous American patriots are funding the ballroom to the tune of approximately US$400 million, which will be a secure and appropriate venue for Presidents for generations to come,” spokesman Davis Ingle said.
An alleged plot to attack the White House during a cage fight attended by Trump and other top officials at the weekend “proves exactly why the East Wing Modernisation Project is severely needed for large scale events,” he said.
Ingle added that the ballroom project was “inextricably tied” to presidential security and other security assets, which Trump says include drone ports on the roof and a hospital in the basement.
In late March, Trump reiterated to reporters that the project would cost up to US$400 million, calling it “tax-payer free.”
However, a summary prepared for the White House earlier that month already estimated the total cost at US$600 million, with only US$293 million coming from “private sources,” the Post said.
And when Trump made those comments in March, the administration had already approved more than a dozen payments of public funds to Clark Construction totalling tens of millions of dollars, the Post said, citing a log of the contractor’s invoices which it obtained.
When Trump first floated the idea of the ballroom he said it would cost US$200 million.
Democratic opponents of the president have pointed to the gilded ballroom and other costly renovation projects around the US capital as evidence that the billionaire leader is out of touch with everyday Americans.
Republicans fear that continued concerns among voters about the cost of living – especially soaring fuel costs due to the Iran war – could spell disaster in the November midterm elections.
“This is a gift to the United States of America,” Trump said last month as he took reporters on a tour of the building site, shouting over the noise of hammers and buzz saws.
“This is all my money and donors’ money. This is tax free,” Trump said.
The builder was quoted by the Washington Post as saying details of the project are confidential.
The project has prompted a legal battle, with a judge ruling in March that work above ground needed to halt.
The ruling was put on hold as an appeals court considers the case.
Trump’s administration has also argued that the need for the ballroom became more urgent after a man with a gun tried to break into a gala press dinner he was attending in April. (AFP)