The president is quoted as saying

  The White House Ballroom is being privately funded by many generous Patriots, Great American Companies, and, yours truly.

Whether that is credible, and whether there is an obligation of financial transparency, is apparently too politicized to dig deeper for The Guardian.

More accurately, the article quotes White House officials:

  Officials said it would be paid for by Trump and unnamed donors.

So far there's been 200+ days of statements by White House officials of the current administration to the press.

Some of those statements have had questionable accuracy, some have been undeniably at odds with reality.

Apparently it's incredible that Biden wasn't a body-double his entire presidency but it's credible that "anonymous donors" are sponsoring a ballroom at the Whitehouse. I call this Schrodinger's presidency...

Being paid for by bribes means it will cost the American populace even more than the $250 billion sticker price.

The source for the source of funding is also mentioned in the article.