A refugee resettlement deal struck with the United States is expected to save Australia hundreds of millions of dollars.
Federal budget papers indicate the government will reduce its spending on offshore immigration detention from $1.1 billion this year to $705 million next year.
Funding will then fall to $327 million in 2019-20 and remain steady for the following two years.
The US has agreed to take up to 1250 refugees being held on Manus Island and Nauru, subject to its own "extreme vetting" of applicants.
The Turnbull government is also banking on savings from scaling down onshore immigration detention, with funding dropping from $797 million this year to $712 million in 2018-19 and $665 million the year after.
In a separate measure contained in the 2018 budget, migrants could be forced to wait up to four years before accessing a raft of welfare benefits.
The government already has legislation before parliament to push the waiting period for various payments out to three years, which it expects will save $1.3 billion.
Migrant and community groups have pushed back hard against the move, fearing it could force some new arrivals into destitution and poverty.
But the government is now proposing to stretch the wait time for migrants wanting to access Newstart and Youth Allowance - as well as various parenting and family payments - out to four years, from July 1.
The extra squeeze on migrants is expected to save an extra $200 million.
Exemptions for vulnerable groups and humanitarian entrants will continue to apply, while hardship provisions will also remain in place.
Meanwhile, newly arrived refugees could also be made to wait six months before accessing Centrelink's job-seeking program.
The change, which doubles the existing three-month wait, is expected to save $68 million over the next four years.
"This measure will improve the sequencing of services available to refugees ... assisting refugees to focus on settlement and improving language skills during the first 26-week period of their arrival," the budget papers say.
Refugees with good English will be able to volunteer for some assistance after six weeks.
Those eligible for job-seeking services will also have access to workplace-specific English language training, as well as the 510 free hours of English lessons they receive upon arrival to Australia.
The budget maintains Australia's permanent immigration intake at 190,000 skilled and family visas a year.
Prime Minister Malcolm Turnbull said the skilled migration program was run according to the national interest and people were no longer getting visas to "flip burgers".
"It's not the quantity of immigrants, it's the quality," he told 2GB radio.
"We do not take one person into Australia who we do not want or need."