Taxpayers will fork out almost $24 billion as part of the Government's commitment to the F-35 Joint Strike Fighter program - almost double the estimate.
Tony Abbott confirmed yesterday the Government would spend $12.4 billion to buy another 58 of the stealth aircraft.
It will take Australia's JSF fleet to 72 planes, with an option to buy up to 100 in future.
Bu the Prime Minister revealed it would cost another $12 billion to keep the planes fuelled and flying. "This purchase is $12 billion for the aircraft and equipment associated with the aircraft and a further $12 billion to keep them operational until 2024," Mr Abbott said.
He waved away questions on when the massive spending would appear in the Budget.
"This is not new spending today in the context of a tough Budget," Mr Abbott said.
"This is spending money we need to spend that has been sensibly put aside in the past to ensure that our nation's defences remain strong."
But defence experts said full funding for the JSF had not been held aside. Instead, successive Budgets simply noted the money would be needed in future.
"No parcel of money has been put aside in a vault for this," Andrew Davies, a senior defence analyst at the Australian Strategic Policy Institute, said.
WA Liberal Dennis Jensen, a long-time critic of the JSF program, blasted the decision to commit fully to the plane. "It's a dud decision," he said. "This aircraft is replete with problems."
Dr Jensen, who worked at the Defence Department's technology arm, dismissed Mr Abbott's suggestion that one aircraft would cost about $90 million, estimating they would likely cost closer to $194 million each.
Defence Minister David Johnston said Australia reserved its right to pull out of the program should costs blow out or the aircraft was shown to be wanting.