Independent MP Andrew Wilkie has questioned Opposition Leader Tony Abbott's judgement in making a $1 billion offer to rebuild the Royal Hobart Hospital, describing it as "almost reckless".

Mr Wilkie yesterday announced he would support Prime Minister Julia Gillard's attempt to form government because he believed Labor would better be able to offer a stable, competent and ethical government.

And he told ABC 1's 7.30 Report Mr Abbott may be regretting making his hospital an offer in light of a potential $11 billion shortfall in Coalition costings.

"I think he might be having a different view tonight about who he should've made that offer to, because as generous as it was, it was almost intoxicating to look at a piece of paper that offered me $1 billion," he said.

"But I very quickly came to the conclusion that it was almost a reckless offer because there was no indication of where that money might've come from; there was no suggestion it was part of some normal process that is in place for raising or for allocating funds.

"And there's also the problem that it was against a backdrop of a big black hole in the Coalition's election promises."

He says Labor's more modest offer of $340 million showed a commitment to process which was lacking in the Coalition.

"That $1 billion was very attractive initially but the gloss soon wore off," he said.

"Now I compare that with the ALP's pledge to allocate some $340 million to rebuild the Royal Hobart Hospital, but that is through the normal process of a grant from the health and hospitals fund.

"So it is abiding by process. It is a more modest and realistic sum at a time when the federal budget is under a little bit of strain and struggling to get back to surplus.

"And importantly, I managed to negotiate something which is quite equitable. By bringing forward the next round of health and hospital fund funding, it means something like $1.8 billion will be released to go to hospitals around the country, including $340 million for the Hobart hospital."

Sticking to their guns

But Opposition finance spokesman Andrew Robb says Mr Wilkie provided the figure and the Coalition was well-placed to fund the rebuild.

"It was on his advice the most important program for his electorate and for Tasmania from his point of view," he said.

"It was Andrew Wilkie who said to Tony Abbott 'We need a new hospital, the state has not got any money and we could need up to a $1 billion to produce that hospital'.

"That hospital - in fact any concessions we seek to make to the various independents... - [will] be paid out of savings that we have identified throughout this budget process."

Mr Robb also contested the Treasury costings of Coalition election promises, which show a potential shortfall of between $7 billion and $11 billion.

"We reject outright that our costings are under threat," he said.

"We had three or four hours with Treasury yesterday... and what we discovered in that discussion was that it wasn't a question in error of costings, there was simply differences of opinion about assumptions."

And he said the $1 billion offer for the hospital remained on the table despite Mr Wilkie siding with Ms Gillard.

"That is now a project that we will factor into our long-term spending program," he said.

Mr Wilkie has also indicated he would be willing to work with the Coalition in the event Mr Abbott is able to form government.

"I'm actually confident that, even if Tony Abbott becomes prime minister, I will be in a position to influence policy and in a position to get some good outcomes for my electorate of Denison," he said.

Keeping mum

The other potential kingmakers are continuing to hold their counsel, telling Sky News they hope to make a decision early next week.

In a wide ranging interview, the independent MPs Tony Windsor, Rob Oakeshott and Bob Katter refused to indicate which way they are likely to vote.

However Mr Oakeshott said the issue of the Coalition's costings would weigh on their decision making process.

"You're going to expect more mistakes in an opposition package than a government package, but somewhere up to a $10.5 billion miss is a big miss," he said.

When quizzed about the role of the Greens in Senate both Mr Winsdor and Mr Oakeshott expressed optimism about their ability to work constructively on rural and environmental issues.

"A lot of people in the country are concerned about the Greens, I'm not. In fact over time I've developed a good relationship with Bob Brown," Mr Windsor said.

"We've got to recognise that every environmental policy is not necessarily bad. I don't agree with everything the Greens do, but I'm not petrified about the circumstances of them being in the Senate.

"I say to the farm groups that these people are going to be in a very prominent position in the Senate for some years. Rather than just write them off as being just anti-agriculture, which in my view they're not, go and talk to them, go and raise the issues."

And even self-described anti-Green Bob Katter said there were areas of policy that he agreed with the Greens on, such as restricting food imports, biofuels and the power of the major supermarket chains.

"I was surprised that there was common ground and very aggressive common ground. That's common ground with us, but not with the major parties I might add," he said.

The political horsetrading is expected to take a back seat today as Ms Gillard and Mr Abbott attend the funeral of the latest soldier to be killed in Afghanistan.