The gambling industry has exaggerated the costs of placing s $1 maximum bet limit on poker machines, a Productivity Commission expert says.

The Joint Select Committee on Gambling Reform held a hearing in Canberra on Friday to investigate the merits of a Greens private member's bill to restrict gambling losses to $120 an hour.

High-stakes poker machines can chew through $1200 an hour.

The Productivity Commission recommended in a 2010 report the $1 bet limit be phased in over time, along with mandatory precommitment technology.

However, assistant commissioner Dr Ralph Lattimore told the committee there had been "significant exaggerations of the real cost" of the proposal.

The gambling industry has estimated the cost of introducing $1 maximum bets at between $3 billion to $5 billion, while the Department of Community Services calculated the cost at $1 billion.

Dr Lattimore said those estimates did not take into account the depreciation of poker machines and were based on immediate timeframes rather than a gradual phase-in periods.

"The cost of doing it the way we proposed would be less than that," he said.

Under the watered-down measures against problem gambling passed by federal parliament last year, poker machines will have to be capable of carrying mandatory precommitment technology by 2018.

Asked whether machines could also be made $1 bet-ready, Dr Lattimore replied, "It wouldn't be difficult from a technological perspective."

"There is no reason you can't have a flexible machine ... it would be valuable from the point of view of lowering the costs of experimentation," he said.

Dr Lattimore said there would be "incremental" additional costs to have machines readied for both the $1 bet limit and mandatory precommitment.