Victorian party leader Warren Pickering on Monday confirmed One Nation would not publish its costings before the election on November 23.
"The policy costings we have done, we are not publishing," he said outside state parliament, alongside his federal counterpart Pauline Hanson.
The minor party would not join Labor and the coalition to make use of the Parliamentary Budget Office for independent costings, he said.
The move would mean voters will not have the full picture when casting ballots, warned Monash University political scientist Zareh Ghazarian.
"(Voters) won't be able to make that informed decision by comparing apples to apples, oranges to oranges," he told AAP.
"They're depriving voters as they won't have access to that data."
Committed One Nation voters were unlikely to look elsewhere on that basis alone, but swing voters might, he said.
Mr Pickering is nonetheless pitching One Nation as the party of transparency, promising to bring the state's finances "out of the dark".
If elected in November, the minor party would track all government expenditure on a publicly accessible website, he announced.
The Your Money website would also host all cabinet documents within 30 days of their final consideration, as pledged in October.
The pledges were "in tension" with the party's refusal to publish costings, La Trobe University political scientist Nicholas Barry said.
But a lack of policy detail was a feature of many populist parties and had not sent loyal supporters running elsewhere, he told AAP.
"Right-wing populist parties are associated more with tapping into a sense of grievance," Dr Barry said.
"Whether or not a voter who's attracted by that is likely to be put off by the absence of policy costings ... is pretty questionable."
The budget office is a relatively new feature of Victoria's politics, established as a non-partisan agency in 2017.
Mr Pickering said there were "great people" within the office, but claimed its projections could not be trusted.
"When has one of their cost projections been accurate in the last decade?" he said.
"We won't be engaging in that until we have an opportunity to blow the books open ourselves."
Dr Ghazarian said its predictions cannot always be accurate, but what matters was all parties submitting to the same body.
"Whether the figures pan out in the longer term is a different question," he said.
Opposition Leader Jess Wilson on Monday said her party's costings would be released in full "in the usual way" before the poll.
She claimed One Nation's expenditure tracker was a transplant of her pledge made years earlier.
Senior Labor minister Anthony Carbines said budget documents would be released to outline the state's finances.
"One Nation can't reveal any of its costings, yet it wants to set up a tracking system to manage everyone else's costings," he told reporters.
The coalition spent the day campaigning on a pledge to spend $200 million funding 335 new fire trucks.
It followed a similar $167 million pledge from Labor in October, which aims to deliver 150 new vehicles by 2030.
Premier Ben Carroll committed $26.9 million to fund extended hours for 10 public dental clinics across the state.
Latest polling ranks the coalition firm favourite to win government with 29.5 per cent of the primary vote ahead of Labor's 22.5 per cent and One Nation's 22 per cent.
The Roy Morgan survey released on Friday also showed a dip in popularity for the Greens, from 14 per cent to 12.5 per cent.
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