A senior NSW bureaucrat says safety modifications on new Korean-made trains which the state government purchased will cost taxpayers a lot less than $1 billion.
The government and Rail, Tram and Bus Union have been in deadlock over safety concerns for passengers with new intercity trains that has stretched to more than a year.
Earlier this month, Finance Minister Damien Tudehope said the union's requested safety modifications would blow out to $1 billion.
But in a budget estimates hearing on Monday, Transport for NSW secretary Rob Sharp said "it's nowhere near $1 billion".
"The actual physical costs are much lower than $1 billion," he repeated when questioned by Labor's John Graham.
Treasurer Matt Kean also raised the alarm on growing costs saying the government was paying $30 million per month it to store the New Intercity Fleet (NIF).
"There's $2 billion worth of rolling stock sitting in mothballs behind me rusting on the tracks because of these unreasonable demands from the union," he said earlier this month.
Mr Sharp contended the costs were under a $1 million for storing them, but noted there were maintenance and contractual costs involved.
The state's budget is due to be handed down on June 21.
Committee chair Greens MP Abigail Boyd described Mr Tudehope's cost estimates as "quite absurd".
The union argues guards on the Mariyung fleet, purchased for $2.8 billion, will not be able to adequately monitor the safety of passengers on platforms as the trains arrive and depart.
It had been negotiating for nearly two months with Transport Minister David Elliott, but talks stalled after Mr Tudehope said the costs were too prohibitive.
RTBU secretary Alex Claassens told AAP earlier this month that Mr Tudehope's figure was "gold-plated" and "inflated", noting the fixes will not "cost that sort of money".
Premier Dominic Perrottet said he was keen for the dispute resolved speedily.
"It has been three years ... and some of these trains have been gathering mothballs for over 12 months," he said on Monday.
"That is unacceptable. These are world class trains and they need to be on the tracks," he said.
Mr Perrottet said he understood the union's concerns and wanted to hammer out a deal.
"My job as premier is to get them (the NIF) on the tracks for the people of New South Wales".
Transport NSW chief operating officer Howard Collins told the committee on Monday the union had requested changes to the bell button, emergency stop button, and modifying the guard's door among a raft of other safety concerns.
The Office of the National Rail Safety Regulator approved the trains as safe in July.
But the union said the safety assessment was conducted by the same company that built the trains, and they had independent assessments stipulating the trains were not safe.
Mr Tudehope said earlier this month the union should raise any safety concerns with the regulator.
