Flinders University health economists on Friday said their modelling suggested five times as many asymptomatic positive cases would begin isolating early if RATs were freely available.

That's compared to a group where 20 per cent of people have bought their own RATs.

"By making rapid antigen tests free, you can encourage people to test earlier before they have symptoms," lead author Professor Jon Karnon told AAP.

"If you haven't got a rapid antigen test, then people are less likely to test before they have symptoms. By the time they have symptoms, they could have passed COVID-19 onto many people."

Each of the models assumes one in 10 people have COVID-19 but are not symptomatic when using a RAT.

Under the free RAT model, the cost of providing a test to a group of 10,000 costs the government $100,000.

But the cost is reduced to about $52,000 when compared to the other model, where far more PCR tests, costing about $150 each, are used.

While the accuracy of rapid tests is lower, the free RAT model would isolate an additional 464 people in the early stage of their infection, thereby reducing costs to the wider economy of further infections, the researchers say.

"The government decides to spend a lot on other areas, where they're getting less value, it seems to us, than they would get from spending money to provide free rapid antigen tests," Prof Karnon said.

The model hasn't been peer-reviewed and the researchers acknowledge overuse or hoarding of free rapid tests would reduce the cost-effectiveness of the policy.

Prof Karnon said the policy would be effective in all states currently experiencing COVID-19 outbreaks.

It currently isn't worthwhile in Western Australia, due to the low rate of COVID-19 in the general population, he said.

Australian Associated Press