Australia's government intends to hold a non-binding plebiscite on whether to allow same-sex marriage, although a date has not yet been scheduled.
The Australian Electoral Commission previously estimated the cost of running the plebiscite at A$158m.
But research by accounting firm PwC said this figure was too low, as it did not allow for "total economic costs".
PwC's report said holding a stand-alone plebiscite on a Saturday would cost Australia's economy $A280m in lost productivity.
Its impact on the "mental health and wellbeing of Australian citizens" would also cost at least $A20m, the report said.
Funding the campaigns for and against the proposal would cost a further $A66m, it said.
"The real costs to government, the economy and members of the community to hold a standalone plebiscite are more than three times higher than the numbers commonly quoted," PwC Australia CEO Luke Sayers said in a statement.
"Total economic costs have not been considered before and should be part of the debate on the best way to achieve a resolution to this issue."
But Liberal senator Eric Abetz, an opponent of same-sex marriage, questioned PwC's methodology in calculating the cost of lost productivity.
"Because, quite frankly, to try to take into account and double the figure on the basis of the time taken to vote as being a factor basically says, 'look, let's get rid of democracy; each time people go to the polling booth it costs them $281m'," he told the Australian Broadcasting Corp.
Senator Abetz has previously indicated that he may not view the results of the plebiscite as binding.
The PwC research said that if a public poll were taken concurrently with the upcoming federal election, rather than as a stand-alone vote, it would cost $A113m.
A parliamentary vote without a public poll would cost $A17m, PwC said.
The stand-alone public vote was initially announced by the former prime minister Tony Abbott.
Malcolm Turnbull said he would push ahead with the plebiscite after replacing Mr Abbott as prime minister last year.
A stand-alone public vote on same-sex marriage would cost Australia $A525m (Â£275.5m; $396m), a new report says.