The government has set aside $160 million for a nationwide vote on marriage equality in the federal budget.
The money is in the Contingency Reserve, which is where funding is held for anticipated events that do not appear in the budget papers.
$160 million has also been set aside for a referendum on constitutional recognition of Indigenous Australians.
In September 2015, the Australian Electoral Commission estimated the cost of a plebiscite at $158.4 million.
The AEC estimation was based on the plebiscite being held at some point in the next year, and on the two opposing campaigns receiving no public funding beyond a pamphlet distributed by the Electoral Commissioner.
While no definite timeline for the plebiscite has been offered, Turnbull said in March that the vote would be held soon after the general election.
Earlier this year, it was reported that plans for plebiscite, including the framework and wording, had been placed on hold until after the election.
Parliament will have to pass a bill before the plebiscite can be held.
Bill Shorten has promised that a Labor government would introduce a marriage equality bill within 100 days if elected in July.
The only other nation to have introduced same-sex marriage via a popular vote is Ireland, which held a successful referendum in May 2015.
With just over 60% of the population turning out to vote, Ireland saw 62% vote in favour of marriage equality and 38% against in a decisive win for the "Yes" campaign.
The marriage referendum was held alongside a referendum on lowering the age of presidential candidates, which failed. Neither campaign received government funding, but two government departments provided €2.7 million to the Referendum Commission to explain the two proposals and encourage voter turnout.
Of that money, the Commission spent €2.2 million. The overall cost of the joint referendums was estimated at €15 million.