In a London Assembly meeting on Wednesday (June 8), TfL Commissioner Mike Brown said the cost would be £680 million, a significant change from the former estimate of £1.9 billion.
He told Assembly members he is "absolutely confident" Khan's plan can be delivered, with funding for the first two years already planned out by assessing aspects of the company including the pay of its highest earners.
Those using single or Pay as You Go will benefit from the freeze, but not daily or weekly travel card users, which some Assembly Members regarded as a "broken promise".
'I don't want to see plans cancelled or damaged'
The announcement drew criticism from Conservative Members, who claimed it was "very fishy" the figures had changed so drastically.
Assembly Member Gareth Bacon said: "I don't want to see it cancelled or damaged, it has changed so radically."
Assembly Member Caroline Pidgeon also critiqued the decision and tweeted: "Mayor's fares freeze promise broken today. Will not apply to travelcards. Not what he said in campaign."
The fare freeze was one of the Labour Mayor's election pledges , but caused a storm after TfL argued a five year plan would cost £1.9 billion , four times as much as Khan had initially set out.
Mr Brown was one of many who criticised the pledge initially, claiming it was not possible and would cripple the city's infrastructure.
'Fares freeze welcome for millions of employees'
Responding to the fares announcement by Transport for London, London Policy Chairman, Sue Terpilowski, said: "The announcement of the fares freeze is welcome for millions of employees within small businesses who face some of the highest transport costs when compared to our international counterparts.
"The major concern for many small businesses is that efficiencies might lead to more TfL contracts being given purely to larger businesses that can deal with efficiencies of scale."