The UK will pay at least £370m to Rwanda as part of its plan to relocate asylum seekers there, the government's spending watchdog has revealed.
Up to £150,000 will also be paid for each person sent to the east African country over a five-year period.
Labour said the new figures in the report by the National Audit Office (NAO) were a "national scandal".
However, the Home Office said: "Doing nothing is not without significant costs."
A spokesperson said: "Unless we act, the cost of housing asylum seekers is set to reach £11bn per year by 2026.
"Illegal migration costs lives and perpetuates human trafficking, and it is therefore right that we fund solutions to break this unsustainable cycle."
The NAO report comes after MPs have been calling for greater transparency over the cost of the scheme.
Under the five-year deal, the UK would be able to send individuals who arrive in the country illegally to Rwanda to claim asylum there.
The aim of the policy is to deter people from crossing the English Channel in small boats - something Prime Minister Rishi Sunak has made one of his key priorities.
However, the scheme has been stalled by legal challenges and no one has been relocated there yet.
The government says it is aiming for deportation flights to take off by the spring.
Legislation seeking to revive the plan has been approved by MPs and will be debated in the House of Lords next week, where critics are likely to seize on the latest costs.
£63,000 more to remove a migrant than keep in UK
What is the UK's plan to send asylum seekers to Rwanda?
Under the scheme, the Home Office has agreed to pay money into a fund to support economic growth in Rwanda, as well as providing extra payments to cover the cost of processing and relocating individuals there.
The UK has already paid £220m into the economic development fund since April 2022, with further annual payments of £50m scheduled for the next three years.
This amounts to a total of £370m over five years.
If more than 300 people are eventually sent to Rwanda, the UK would pay a one-off sum of £120m into the fund, with further payments of £20,000 per individual relocated.
On top of this, the UK government would also provide up to £150,874 per person to cover costs such as accommodation, food and education.
These payments would stop if the individual chooses to leave Rwanda, with the UK instead paying £10,000 per person to facilitate their departure.
The NAO's report also reveals that the cost of setting up the scheme could rise from £20m to £28m.
There are also expected to be other future costs, including an estimated £11,000 per individual for flights to Rwanda.
The NAO does not come to a judgement on whether the scheme is value for money as the watchdog said this would depend on whether it is successful in deterring people from coming to the UK illegally.
Labour has pledged to scrap the Rwanda policy if it wins the next election, describing it as an expensive "gimmick".
Shadow home secretary Yvette Cooper said: "This report reveals the national scandal the Tories have been trying to hide.
"Its shocking analysis shows the costs of the failed Rwanda farce are even higher than previously thought."
The report was produced in response to a request from two cross-party committees of MPs - the Public Accounts and Home Affairs Committees.
In December the Home Office's most senior civil servant wrote to the chairwomen of both committees to reveal some of the costs associated with the scheme but they said this did not provide enough information on how much had been spent so far.
