BBCThe ninety minute debate involved the leaders of the six largest partiesReform has challenged all the main parties to publish the full costs of their promises to voters ahead of next week's Senedd election.
None of the six larger parties have released full details, with independent analysts criticising the lack of transparency on how manifesto pledges would be funded.
On BBC Wales' Your Voice Live: The Leaders' Debate Reform's Dan Thomas said he would publish his party's plans if the others followed suit.
Labour's Eluned Morgan and Darren Millar said they were prepared to, while Plaid Cymru's Rhun ap Iorwerth said his party had published "many of the costings".
Green Anthony Slaughter said his party had revealed some costings while Liberal Democrat Jane Dodds said she would not as her plans were about "ambition".
Meanwhile four party leaders on the left ruled out working with Reform - but not each other.
Voters in Wales go to the polls on Thursday 7 May to elect 96 Senedd members from 16 constituencies.
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The Institute for Fiscal Studies (IFS) says the in-coming Welsh government will face a severe financial squeeze, with day-to-day funding and investment growth slowing significantly.
The experts warn that many of the manifesto pledges by the parties will be likely to require tax rises or cuts to public services.
In the sometimes bad tempered live BBC1 TV debate, the calls for the leaders to fully publish their spending plans were greeted with a round of applause by the studio audience.
The leader of Reform UK in Wales, Dan Thomas, said he would publish his plans if the others would follow suit: "I challenge every leader on this panel to publish your costings.
"Ours are ready to go so we can have a full transparent election."
Welsh Conservative leader Darren Millar said he was "quite happy" to answer questions on costings.
"And I'll tell you what, if everybody else publishes theirs I'll be very happy to publish ours."
The Welsh Labour leader and first minister said: "You know, I think it's all very transparent [Labour's pledges]. I'm happy to show you what we've got and listen to what we've go."
Plaid Cymru leader Rhun ap Iorwerth said: "We have published many of the costings, because it's really important that people can see how we put together a programme for government."
Wales Green Party leader Anthony Slaughter said some of his plans had been costed.
"So that's things like a rent freeze leading to rent controls," he said. "That's things like free bus travels for under 22s, £1 for everyone else."
Welsh Liberal Democrat leader Jane Dodds said she would not publish her spending plans.
"I am being as honest as I can and it's a no, because our manifesto is about ambition and aspiration," she said.
"We want to influence government, I'm not going to be first minister on the eighth of May."
In the debate, Reform's Dan Thomas was asked by presenter Bethan Rhys Roberts whether he "distanced" himself from a social media comment made by a prominent member of the party, Arron Banks, which sparked accusations of racism from Plaid Cymru.
Banks is not standing in the Senedd election and told BBC Wales that his comment was " a joke" adding that "Plaid have understandably lost their sense of humour".
Thomas did not respond directly but said: "I've had my Welshness questioned by supporters of Plaid Cymru. They've called me a plastic Taffy because I happened to live in England.
"I've been called an English nationalist, because I happen to be a member of Reform. I am Welsh through and through".
Plaid Cymru leader Rhun ap Iorwerth criticised Thomas' response: "Outright racism from a righthand man of Nigel Farage and Dan Thomas chooses to play the victim".
Four party leaders ruled out working with Reform
No party is expected to win a majority and some level of co-operation will be needed to form the next Welsh government - whether that's a coalition or something else that helps a government get its business through the Senedd.
Leaders of Plaid Cymru, the Welsh Liberal Democrats, Labour and the Greens said they could not work with Nigel Farage's party - but did not rule out working with each other.
There were calls for parties on the left to work together to lock Reform out of power from former first minister Mark Drakeford earlier in the campaign.
Plaid Cymru's Rhun ap Iorwerth said Reform stood in "diametric opposition to all the values that I stand for".
Eluned Morgan said she did not think Labour had "enough in common" with Reform to be working with them.
Anthony Slaughter said the Greens will not work with "Reform or the Conservatives in any shape or form".
He said he agreed with comments by the UK leader that it would be a "relief" if Plaid did well in the election.
Jane Dodds said the Lib Dems would also not work with Reform or the Tories.
"We are willing to be a responsible partner to stop Reform UK trashing our services," she said.
Dan Thomas, leader of Reform, said they would work with any party "that will help deliver our manifesto".
He accused Labour and Plaid of stitching up the new voting system for the expanded Senedd "to make sure they end up in power one way or another".
Darren Millar also would not rule out working with Reform or any party, saying he would work with any party that could help deliver Tory policies like cutting income tax.
'Wales is crying out for change'
In his closing statement in the programme, Ap Iorwerth said that Wales "can't risk handing power to Nigel Farage.
"One party must be larger than Reform - that can only be Plaid Cymru."
Millar said "Plaid does not represent change" after keeping "Labour in power for decades".
The Welsh Conservatives offered "real change" and "positive change", he argued.
Dodds said she believed Wales is "better than the nasty politics that Reform UK want to import from Donald Trump's America".
"There are places up and down Wales where the Liberal Democrats are best place to stop at reform UK," she added.
Slaughter said "Wales is crying out for change" and that under the new voting system voting Green will get Greens.
"And every one of them will need one less Reform member, with their hatred and division," he said.
Thomas promised Reform would "unite Wales around our common sense policies and the principle of putting you, the people at home, first".
"Plaid Cymru will divide Cymru by pushing for independence, and we all know they will do a back room deal with Labour," he warned.
Morgan said "other parties want you to take a risk" but "Welsh Labour have a credible plan".
"Ask yourself, do Plaid Cymru's policies add up, is the NHS safe in reforms hands?"
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