The UK's national ID scheme will cost £5.4bn to set up and run over the next 10 years, the Home Office says.
The ID card scheme will be introduced 'rapidly'
It is the first time the government has set out the estimated total expense for the controversial project.
Ministers claim ID cards will help in the fight against illegal immigration and terrorism.
But the Tories, who want the scheme scrapped, say the true cost is likely to be £20bn and the cash would be better spent on building more prisons.
'Will do nothing'
Shadow Home Secretary David Davis said: "The Home Office has an absolutely appalling record for delivering IT-based projects on time and on budget.
He said ID cards would "do nothing" to improve security and "may make it worse".
"What the government should be doing is answering our calls to establish a UK border police, putting more police on the streets and appointing a dedicated minister to co-ordinate our security efforts," added Mr Davis.
Liberal Democrat home affairs spokesman Nick Clegg said the public had "every right to maintain a healthy scepticism about this figure".
The ID card scheme will force every adult in the UK to pay for a "biometric" card which stores fingerprint and iris scan details.
Leaked e-mails earlier this year suggested civil servants had serious doubts about whether the scheme could be implemented.
Two weeks ago it emerged that the government would attempt to save cash by using existing government databases to introduce the ID scheme.
Ministers are wary of opting for a single "big bang" solution, favouring instead a series of smaller IT contracts.
But Home Office minister Liam Byrne insisted ID cards would still be introduced "rapidly", with the first biometric cards coming into use in 2008, for foreign nationals wanting to work in the UK.
Speaking at the Institute of Public Policy Research (IPPR), he said ID cards would make illegal working by immigrants "far more difficult".
Mr Byrne added: "Any employer would be able to check a person's unique reference number against registered information about their identity to find out whether someone is eligible to work in the UK.
"ID cards will give us a powerful tool to combat identity fraud which underpins organised crime, terrorism and abuse of the immigration system.
"ID cards will also help transform the delivery of public services to the citizen, making interactions swifter, more reliable and more secure and helping to reduce costs by eliminating wasteful duplication of effort."
However, Shadow Immigration Minister Damian Green said: "First ministers claimed ID cards were needed to combat benefit fraud, then to guard us against terrorism, then to fight identity fraud.
"Having lost these arguments they now they claim they will be used to combat illegal immigration."