A HOLE in the opposition's election costings of at least $7 billion has put a dent in Tony Abbott's bid to form a minority government.

The finding by the federal Treasury, as revealed to the three independent MPs yesterday, has forced at least one of them - New England MP Tony Windsor - to question his possible support for the coalition.

Mr Windsor has urged the coalition to explain the discrepancy in estimated budget savings - as unveiled by Treasury - which stands between $7 billion and $11 billion.

While refusing to say if it will sway his final decision, Mr Windsor said it has made him suspicious about Mr Abbott and whether the coalition can be trusted.

"We probably understand now why he wasn't interested in releasing the numbers,'' Mr Windsor told ABC Television.

"One of (the) things that we have to establish is trust in what they're actually saying.''

Fellow independent Rob Oakeshott claims the jury's still out on the coalition's costings.

Labor has seized on Treasury's assessment, accusing the coalition of either "deliberate dishonesty or incompetence, or both''.

Treasurer Wayne Swan said there were problems with the coalition's sums relating to the national broadband network, which it wants to scrap, and an undercosted paid parental leave.

"These are mistakes and deliberate dishonesty,'' Mr Swan told ABC Radio.

But the opposition was out in force on Thursday, arguing its figures still stood up to scrutiny.

"It's a matter of difference of opinion, it's not a matter of error,'' opposition finance spokesman Andrew Robb said, arguing Treasury used different models and data in its assessment.

Opposition treasury spokesman Joe Hockey denied the costings debate would sway the independents against the coalition, saying he'd already spoken to Mr Oakeshott.

"We stand by emphatically our policies and our numbers,'' he said.

"We think we are absolutely right on these figures.''
 
Mr Hockey said the coalition and Treasury agreed on "96 per cent'' of the figures, although Mr Hockey is expected to return to Treasury in a bid to clarify the discrepancies.

Mr Windsor, Mr Oakeshott and fellow independent Bob Katter remain in Canberra today as they attempt to make up their minds about the next government.

Along with independent MP Andrew Wilkie, it's hoped they will come to a decision by early next week.

Meanwhile, the coalition are still battling to woo WA Nationals MP Tony Crook, who maintains he'll sit on the crossbenches if he doesn't get millions of dollars for regional infrastructure.

"Mr Abbott has my phone number,'' he told ABC Radio.