The Department for Transport (DfT) said the research into the feasibility of a fixed link cost £896,681.
Network Rail chairman Sir Peter Hendy led the investigation, which found that a bridge would cost £335bn, while a tunnel would require a budget of around £209bn.
In addition to the huge expense, the inquiry also noted that the necessary work would be incredibly challenging.
The report described how Beaufort's Dyke - an underwater trench on the most direct route between Scotland and Northern Ireland - would need to be "carefully surveyed" due to a million tons of unexploded munitions being dumped there between the First World War and the 1970s.
Mr Johnson previously talked up the creation of a fixed link but accepted the conclusion of the report.
The research was carried out alongside a wider review of connectivity in the UK, which cost £1,102,525.
The DfT said the total of £1,999,206 for both studies was the amount spent on consultancy fees and department staff costs.
Sir Peter led the review alongside his role at Network Rail and did not receive additional pay.
Willie Rennie, economy spokesman for the Scottish Liberal Democrats, said: "This is a gobsmacking sum to have spent on a PR stunt. It sounds like something that the Prime Minister came up with at 2am at a Downing Street party."
He added: "This is money that could have been spent on health, education and support for businesses. This bridge stunt is yet another example of Boris Johnson having fun at the expense of the taxpayer. He's totally unfit to be Prime Minister and should step aside."
SNP MP Mhairi Black said the bridge was an "unworkable, doomed from the get-go idea", and added: "This just goes to show the Tories' warped spending priorities. How many lateral flow tests could this have bought, or nurses' salaries paid, or PPE purchased for those on the front line in this pandemic?
"However, as daft as this idea was, it still promised to put £20bn of investment into the Scottish and Northern Irish economies. The Prime Minister must honour the spending commitments he made and deliver that money to Scotland and Northern Ireland so they can use it for worthwhile infrastructure proposals.
"The UK Government said it was 'deadly serious' about these proposals - it's time to come good on its words and deliver the investment."