The NBN debacle will be dwarfed by the submarine project.
The total cost of the project is budgeted for $50bn with an extra $5bn-$6bn allocated for weapons.
The first sub won’t be battle-ready until 2034 after which Defence expects to roll one out every two years. Australia will not receive its full complement of boats until the 2050s.
Allow 100% cost blowout and a decade or two on the delivery. The upside is that it will all be academic, apart from the addition to the national debt, because they will be out date for the next war long before they become a target.
Thinking laterally to save some money. Since they are only likely to be used for target practice by the enemy forces, why not leave out the engines and weaponry and just build shells to tow behind some other vessel as decoys to draw enemy fire?
UPDATE A comment by a longtime observer of the submarine fleet.
I disagree with the comment about buying US submarines, they are all nuclear and setting up the infrastructure to handle them would be way more expensive than a whole fleet of conventionals. We should have bought stock standard, off-the-shelf German boats. We would have had the whole lot in 10 years for about a quarter the cost. The difference in cost comes about from having to make a unique design to accommodate a US combat system, plus the cost of paying the US to actually develop a combat system for a conventional boat. Their first go was the disaster in the Collins Class.