A parliamentary committee examining the 2025 election is also reviewing whether Australia needs more MPs as the population increases and representatives are responsible for an increasing number of constituents.
Each electorate covers about 120,000 voters, and thousands more constituents not on the ballot, with the area of some regional seats bigger than European countries.
Opposition Leader Angus Taylor put the figure for the expansion at $620 million, including salaries, staff, travel and office costs, as calculated by the Parliamentary Budget Office.
"At a time when Australian families are tightening their belts, the last thing they should be asked to fund is more politicians," Mr Taylor said.
However, this doesn't account for any increase in staff needed to fill extra demand currently, as crossbenchers and opposition members have consistently complained about inadequate staffing, which is controlled by the prime minister, to do their jobs.
The coalition's announcement has front-run the inquiry and while accusing Labor of being focused on expanding parliament, the government hasn't modelled numbers or figures, instead saying it would wait for the committee's findings.
Labor can still pass laws increasing the parliament without coalition support, with a supportive crossbench in the Senate and a majority in the lower house, but Special Minister of State Don Farrell has signalled he wanted cross-party support on the issue.
Senator Farrell has had ongoing talks with the opposition and other parties but was clear he wouldn't act before the committee's findings, a Labor source told AAP.
"The only party that appears to have done the numbers on expanding the parliament is the coalition," the source said, accusing the opposition of hypocrisy for Labor was too focused on the issue rather than cost of living.
The parliamentary committee has heard evidence of the need to expand parliament to keep up with demand from constituents, as well as the need for fairer representation for the territories, which only have two senators compared to each state's 12.
Election analyst Kevin Bonham flagged a potential expansion to 14 or 16 senators per state, which would add about a dozen seats to the 150-strong lower house due to proportionality requirements.
Independent ACT senator David Pocock is pushing for territories to have four senators to boost representation, saying the point of the upper house was to balance representation between bigger and smaller states and give the latter a more equal voice.
For example, Tasmania has 576,000 people - as at September 30, according to the Australian Bureau of Statistics - and 12 senators, while the ACT has 486,000 people and two upper house members.
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