Look at what they actually cost: £149 million per ship, i.e. AUD240 mn, of which a large proportion was wasted. If they'd all been built at BAe Govan, or another yard which wasn't failing & needing to be propped up, having lost a lot of skills (leading to various costly problems), & with a workforce aware that the yard would close when the contract was complete, I reckon they'd probably have come in somewhere near £100 mn each, allowing for an overrun on the original contracts (£332 mn, IIRC).
Update for inflation, & you get about AUD200 million.
The price of US naval ships is not a good guide to what it would cost to have a ship built elsewhere. Also, the Harpers Ferry class is slightly bigger, faster, has far more weapons, a bigger dock, & several times as large a crew, with accommodation for twice as many personnel altogether, including troops. It may well be an inferior sealift ship (e.g. less cargo space, less manoeuverable in tight harbours) , but it looks more complicated, & hence expensive, in some ways.
