Eradicating weeds and replanting vegetation were among the costliest species-saving interventions identified in university and environmental group research.
Australia has one of the world's highest loss rates and is vying to stop new species going extinct, with federal government outlining a game plan back in 2022.
Tuesday's research from Griffith University, WWF-Australia and the University of Queensland, found it would cost $15.6 billion a year over 30 years to stop 99 priority terrestrial and freshwater species going extinct.
Marine creatures were not included.
Lead author Michelle Ward, from Griffith University, said the researchers tallied up the full suite of actions needed to ensure species have enough habitat - at least 100 square kilometres - to stay off the the critically endangered list.
"Like, if a trout is getting into a stream and it's eating the little native fish, then we costed the specific action of what is needed to mitigate that trout," she told AAP.
"Most shocking" for Dr Ward was the discovery 16 species could never be removed from the threatened species list due to unmanageable threats like climate change, no matter how much money was spent.
"Species such as Mountain-top Nursery Frog and Swan Galaxias were found to be of real concern and need active ex-situ conservation," she said.
Dr Ward commended the federal government's commitment to nature and ending extinctions but stressed more funding was needed.
WWF-Australia's head of evaluation and science Romola Stewart said the purpose of the research was to present governments with realistic costs they could use for budgeting and resourcing.
Dr Stewart said it was clearly not sustainable to continue to degrade ecosystems, noting halting extinctions was a "pretty low bar" and getting species off threatened lists entirely would cost even more.
Eradicating weeds and replanting vegetation is a costly way to save species from extinction. (Alia McMullen/AAP PHOTOS)
"These figures are astronomical," she told AAP.
"We obviously can't bear this cost going forward, so we need to stop and halt loss of nature."
Dr Stewart said the research highlighted the true cost of "inadequate" nature laws failing to stop the loss of habitat.
Labor promised to overhaul the way the country manages environmentally risky development, including setting up a watchdog to assess applications independently and act as a cop on the beat.
Yet the government's environmental protection legislation has again been shelved, reflecting pressure from mining interests in the key battleground state of Western Australia.
Minister for the Environment and Water Tanya Plibersek says the government is spending more than $550 million to better protect threatened native plants and animals.
