Downing Street said taxpayers would benefit once flights to the African nation get underway.
The cost of processing and housing asylum seekers in hotels has hit £8 million a day.
But the Prime Minister’s deputy spokesperson said the deterrent scheme will “put an end to the unacceptable costs that we face in the UK every single day.
It has emerged Britain forked out an extra £100 million to Rwanda this year – on top of the £140 million already paid – before any asylum seekers have been deported to the country.
The payment, which had not been previously disclosed, was agreed in April as part of the deal under which illegal migrants relocated from the UK will claim asylum in the Commonwealth nation.
The Government expects to pay Rwanda a further £50 million next year, taking the total to £290 million.
Tory MP Jonathan Gullis said believed the scheme would benefit taxpayers in the long-run once it gets underway.
He said: “I do think there will be value for money when we get people over to Rwanda because that deterrent factor is key in stopping the boats.”
The MP added this “sends the message that you will be detained, you will be removed”.
No 10 insists Mr Sunak did not mislead MPs over the cost of the asylum scheme.
The Government remained tight-lipped on costings as it set out plans to revive the deportation scheme earlier this week, with the further payments only disclosed on Thursday evening in a letter from the Home Office’s top civil servant, Sir Matthew Rycroft, to committee chairs.
But No 10 rejected any suggestion that the Prime Minister had misled, even inadvertently, parliamentarians over the money for Kigali.
The PM’s deputy spokesperson said the original memorandum of understanding with Rwanda stated that the deal “involves subsequent funding”.
“It was always set out that there would be funding attached to what is an economic and migration partnership. And this further funding was part of that,” she said.
The extra £100 million payment, made in April, was signed off by sacked home secretary Suella Braverman, Downing Street said.
Opposition parties reacted furiously to the disclosure, with the Liberal Democrats branding it an “unforgivable waste of taxpayers’ money”.
“The fact that this Government is content to squander millions on this totally unworkable white elephant of a policy tells you everything you need to know about their priorities,” Lib Dem home affairs spokesperson Alistair Carmichael said.
The chairwoman of the Public Accounts Committee, Dame Meg Hillier, hit out at the lack of transparency over the costings, saying they had only been revealed after repeated inquiries.
She told BBC Radio 4’s Today programme that it “almost looks like the Government has got something to hide”.
Sir Matthew has been summoned to appear before the Public Accounts Committee on Monday, a day before MPs vote on the Government’s Rwanda legislation.
“Full and frank answers” on the costings of the deportation scheme are expected from him, Home Affairs Committee chairwoman Dame Diana Johnson and Public Accounts Committee chairwoman Dame Meg Hillier wrote in a letter to the top civil servant.
