Recovering the Pike River mine drift could cost up to $51 million, more than double the original budget.

The Government has approved another $10.8m to complete the project as well as a $4.2m contingency.

The agency was set up in January 2018 to re-enter the drift of the West Coast mine with the hope of finding out why 29 men died in a series of explosions in November 2010.

The Government originally budgeted $7.6m a year for three years, totalling $23m. It then topped up the budget to $36m.

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Pike River Recovery Minister Andrew Little announced on Tuesday that Cabinet had approved final funding for recovery.

MONIQUE FORD/STUFF Andrew Little has announced $15m more for Pike River reentry.

Little also confirmed the recovery effort would not go beyond the end of the drift and into the mine workings, as had been the scope since the start of the project.

"It is important to promote accountability for what happened, to inform the ongoing criminal investigation into the tragedy, and to help prevent future tragedies," he said.

He expected the underground recovery work to be completed by July or August, and the mine site to be handed over to the Department of Conservation.

A new track up to the mine, where a memorial will be built, will become part of the new Paparoa Track Great Walk.

A Cabinet paper by Little says the agency staff had reached up to 315m of the 2.3km drift, or access tunnel. They had not found any evidence or remains yet.

"While work is continuing underground, and on the remediation of the site for handover to DOC, expenditure of $1.3 million to $2.0 million each month will be required to meet the costs of operation," it says.

It says Little had ruled out bringing any proposal to cabinet to move beyond the roof fall at the end of the drift and explore the main mine workings because initial assessment by the agency suggested it would cost another three years and at least $50m more.

The Family Reference Group, which works with the Pike River Recovery Agency, said the budget increase showed how serious the Government was about achieving justice for the 29 men killed at Pike River.

Pike River mother Sonya Rockhouse said the reentry project, and the evidence it could unearth, was the best chance families had to see someone held to account for killing their men.

SUPPLIED Pike River Recovery Agency staff open and walk through doors at the 170m seal. (Video first published December 17, 2019)

Pit bottom and stone is an area off the drift that holds electrical equipment that could reveal a cause of the explosions.

"When we get to pit bottom and stone at the far end of the drift we can start to figure out exactly what caused the explosion that killed my son Ben," Rockhouse said.

"If it's proven to be the result of unlawful actions by Pike management then the next step is prosecutions.

"People ask me why so much money is being spent, to me it's quite simple: it's being spent to try to solve the mass homicide of 29 men. We can't be a country that refuses people justice because it costs too much."

Pike River widow Anna Osborne said the Government's plan to close the door on reentry of the mine workings was "premature".

"It seems a bit odd to say no to that before we have got to the end of the drift and assessed whether reentry of the mine workings is needed or even possible," she said.

She called for other families to campaign for reentry of the mine workings.

Iain McGregor/Stuff Flames coming out of a ventilation shaft at Pike River Mine after a fourth explosion in 2010.

Rowdy Durbridge, whose son Dan died in the mine, said he was proud of what the families had achieved for their boys.

"I had family and mates die in that mine. I worked beside them down there and I've felt a responsibility to them ever since," he said.

"That's feeling's never going to go away but having fought and won drift reentry and the investigation of their deaths, that's something I think me and the families and a whole lot of Kiwis who believe in justice can hold our heads high about."