Sports Minister Trevor Mallard met National MPs yesterday to brief them on the waterfront stadium proposal, but they remained unconvinced that it was a good idea.
Mr Mallard said there was an "outside possibility" the cost of a waterfront stadium could rise to $650 million.
"We've been givenby quantity surveyors a figure of just under $500 million. My view and the advice I've had is that on major projects they are notoriously unreliable, and that people would be best to do a plus or minus - and normally plus - 30 per cent, so that takes it up to an outside possibility of $650 million.
"Even in an Eden Park scenario though, the plus or minus wouldn't be the same because they are further advanced, but there is a big margin in that one too."
He said he had a romantic attachment to Eden Park.
"My gut feeling for a long time was that an upgrade of Eden Park would be the best thing to do. So if Aucklanders decide that that's the approach, then I will back it."
He said North Harbour Stadium was "clearly the third option within Auckland".
"I think there is a lot of work to do on transport connections, and there's also not the infrastructure around the North Harbour Stadium that you have around downtown or Eden Park."
National deputy leader Gerry Brownlee said there was nothing new in the briefing from Mr Mallard.
"What we learned is that it's possible to build it, it's possible to tax to pay for it, but it's impossible to work out how much it's going to cost."
In Auckland yesterday, the tourism industry announced the formation of the Coalition Against Travel Taxes in a bid to stop any proposal to tax travellers to finance a stadium.
