Anything with "N" in it is expensive, takes many years and overruns - same in every country.
Problem in any democracy is that the political horizon is max 4 years - and all that money sloshing about is very tempting for those who wish to buy votes (sorry - meet the concerns of their core supporters of course)
Dutton's plan at least gets a capability in place for (relatively) little money - certainly cheaper than going the "interim" route even I'll bet.