National will charge new arrivals at the border for their quarantine stay almost immediately if it forms the next Government.
COVID-19 border response spokesman Gerry Brownlee said it'll be enough to "partially meet the costs" of their 14-day stay in quarantine or managed isolation.
"Currently taxpayers are funding a long and very expensive Government response to let people come into the country," he said on Sunday. "It's entirely fair that those who benefit pay a share."
From October 3, National wants single adults charged $3000 each. Each additional adult in a room will be charged $1000 and children $500. Under-threes won't have to pay.
Brownlee said there will be "certain exemptions to ensure compassionate consideration.. and in cases where they are facing financial hardship".
"This fee is for the purpose of cost recovery to reduce the burden on New Zealand taxpayers, and to cover some of the costs of accommodation and food over the 14 days of required quarantine for persons entering the country."
He said it's "broadly the same" as quarantine policies in place across Australia.
"National's policy is about fairness. Many Kiwis have only one or two overseas holidays in their lives. National won't expect taxpayers to pay for other Kiwis returning from high-paying careers or expensive holidays in Europe.
"Those who need to return to New Zealand have had plenty of time to get home since border restrictions began, including through repatriation flights organised by the Ministry of Foreign Affairs. They will have a further two weeks to get home without facing the charge, after the election of a National Government."
He said the current cost is about $4000 per person, which has so far been covered by taxpayers.
The Government said in June it wasn't clear whether the Government could legally charge people, since they have a right to return home.
"What we have to make sure is that we're getting that fine balance of fairness between the inalienable right of New Zealanders to come home - and I think we all want to know we will always have that right - against the fairness to the taxpayer," said minister in charge of the border operation, Megan Woods.
"We all need to remember that this money we're spending - and it is a lot of money - is our very strong line of defence that is protecting the position that we got through our sacrifice."
Prime Minister Jacinda Ardern said it's "not a simple thing to work through".
"This is the only place many people can legally reside, so if you put up a wall and say 'you cannot come home' or place up barriers to coming home, that does have legal implications for us."
The borders have been closed to all but returning Kiwis - with a few exceptions - since March.
International law says citizens of any country can't be denied the right to return there, and the Taxpayers' Union last week said it would be "probably unconstitutional" to charge people for a Government-mandated stay in a hotel.
Brownlee said the finer details of the policy would be "informed by common sense".
'Why should citizens be forced to pay an incompetent Government monopoly'?
National's new policy has been rubbished by its potential coalition ally ACT. Leader David Seymour said Kiwis shouldn't be forced to pay a "poor quality, Government monopoly", arguing that private enterprise should take over managed isolation and quarantine under strict regulations.
"A smart, innovative Government would set up a regulatory framework for private provision. Private providers would offer safer, cheaper managed isolation," Seymour said.
"Many of our hotels are going broke and Air New Zealand is being paid not to fly. Instead, Air New Zealand and hotels could offer a private managed isolation package to essential workers and others prepared to pay and wait for time in COVID-free Kiwi paradise."
He argues that universities running hostels and Recognised Seasonal Employer employers required to provide accommodation at a certain standard should be trusted to bring students and workers in under strict rules, administered by WorkSafe with appropriate penalties.
"Allowing private providers to offer managed isolation would also expand our capacity. We risk the economy slowly grinding to a halt as projects of all kinds wait on essential workers from overseas, unless we find a way to safely reengage with the world.
"There's no doubt New Zealanders will have to contribute to the cost of managed isolation, but why should citizens be forced to pay an incompetent Government monopoly?"