Boeing has reportedly forked out US$1 million (S$1.43 million) and oil giant Chevron US$500,000.
The names of other big donors are not yet known, but what is obvious is that the Trump team may be planning a relatively modest Inauguration Day, even though it has raised a record US$90 million for the occasion.
This eclipses the US$55 million spent during Mr Barack Obama's inauguration in 2009, and the US$43 million in 2013.
The black-tie balls and associated parties are funded by private donors. Large sums such as US$1 million can offer special access to, for instance, a candlelit dinner with a chance to hobnob with the president and vice-president.
Taxpayers will foot the bill for the actual inauguration, though - the stands, chairs, portable toilets, parade and security.
Overtime pay for the Capitol police, a separate unit, alone will be US$2.5 million.
Tax money pays for the US$1.25 million expenses of the Joint Congressional Committee on Inaugural Ceremonies. In 2009, spending by the military's inaugural joint task force and the Defence Department totalled US$21.6 million, according to Associated Press reports.
The influx of people for the event - including protesters who this time around may outnumber inauguration and parade attendees by two to one - brings an economic boost to the capital as well.
George Mason University's professor Stephen Fuller estimates that protesters coming for the weekend's events following Friday's inauguration will, ironically, spend US$330 a head.
Those attending the inauguration are likely to stay longer and splurge more on hotels, limousines, eating and shopping.
Prof Fuller estimates they will spend US$3,500 a head.