Wow, Dave, crazy.
Prius non plugin to model 3 is 3x in Australia ? That's really really crazy. What is this cost difference coming from ? is the vehicle tax so damn non-linear ?
In Austria (Not Australia), the Prius PHEV costs the same than the model 3, and the non plugin is probably like 1.4x
In france whee I live, it's like base prius is 30keuro, base model 3 is 40keuro, so 1,3x only. After 5 years, the model 3 is cheaper to own than a VW golf diesel or gas !
Now where you're wrong is that the cost of batteries is dropping 25% or so every year, and the incentives are in the 10% range, so incentives typically only boost EVs one year, depending on countries.
Now Dave, don't worry, cost parity with ICE will come in 3-4 years for the mid-range cars, and that's purchase price. TCO per km for 5-8 years are already lower in a lot of countries.