The Palaszczuk government won't prioritise the project despite increasing its infrastructure spend in next month's budget to $45 billion over four years, the highest level since the 2011 flood recovery.

It has instead put its focus on the Cross River Rail project and a long-awaited upgrade to the Pacific Motorway. The state opposition has promised to forge ahead with the second M1 if elected.

Both major parties have contrasting views about its cost, with Labor valuing it at more than $2 billion but the Liberal National Party opposition is confident it can be delivered for around $1 billion.

Steve Abson, of the Infrastructure Association of Queensland, says an accurate figure for the road between Stapylton and Nerang must be established via a study funded in the budget.

"That would be a really prudent step," he told AAP.

"Rather than guess whether it's anywhere between a billion and $2.4 billion, which is obviously a wide range, we need to invest in a business case to properly assess what the cost-benefit really is.

"Then both sides of the House can make informed decisions."

Mr Abson said failure to do so would see the project incomplete in the next five years, which is contrary to Infrastructure Australia's recommendations.

State Treasurer Jackie Trad also revealed on Sunday no money in the budget would be put toward the Sunshine Coast rail duplication despite the promise of federal funds in the next five years.

"If they're saying they don't want to match it, it would be disappointing because that particular project has a very strong business case. It does stack up," Mr Abson said.

Australian Associated Press