Western Australia's premier has defended a billion-dollar public transport blowout as he looks to taxpayer-funded "fairness fighters" to protect the state's GST share.
State budget papers this month revealed additional cost pressures on four projects within the Labor government's prized Metronet rail expansion network.
The state and federal governments will jointly spend an additional $1.2b across the next three years to complete the Morley-Ellenbrook rail line, Thornlie-Cockburn link, Yanchep rail extension and Bayswater station projects.
Mr McGowan, who unveiled a projected $4.2b surplus in this year's budget in his capacity as treasurer, said the infrastructure blowout was "regrettable but unavoidable".
He told a parliamentary budget estimates hearing the cost hikes were marginal compared to major increases in Victoria and NSW.
"Our rail projects are significantly, like massively more affordable," the premier said.
"The major reason is we plan ahead."
Quizzed by Liberal leader Libby Mettam on whether the overall cost of Metronet could blow out beyond $11b, Mr McGowan declined to rule it out.
"I can't rule out cost increases because that's just the nature of the market we're in," he said.
"We have doubled the number of projects since the original commitment ... some of those projects are very significant.
"It's a much more comprehensive program than it originally was."
Mr McGowan said the projected number of migrants expected to move to WA had doubled within the last six months to more than 36,000 amid significant efforts by the state government to attract workers.
He expected that to ease pressures in the heated building market which have forced the government to push back the delivery of some projects.
"Naturally there will be some greater capacity to build things," he said.
The state government has also allocated $1.6 million for Treasury to hire three new full-time equivalent staff dubbed "fairness fighters".
They will be tasked with developing a business case for WA to retain its existing GST revenue share before upcoming federal reviews.
The funding will cover the wages of the three staff across several years, as well as a consulting budget.
Mr McGowan argued it would be irresponsible not to fund the program given what was at stake.
"In the overall scheme of things, it's a very small investment," he said.
