There is a good reason SA has such high prices, and it is nothing to do with solar and wind power- it is the big gas generators ripping money out of people by gaming the system.
Average South Australia wholesale prices in the first four months of 2017/18 were actually lower than the coal-dependent states of Victoria and NSW (I don't have any more up-to-date numbers handy), and that is likely to continue as more wind, solar and storage is developed.
There's a cool video about the end of coal for SA here:
I'm not sure how old those LCOE numbers are, but electricity from new coal generators, especially with the laughable "low emissions" tag, is going to cost a lot more than $80-90. Even old coal wholesale prices are often running above that now, typically around $100/MWh.
Also, I think you'll find those LCOE numbers for solar and wind are woefully out of date, contracts are around $60/MWh or less for wind in Australia, right now. Solar isn't much more.
One developer, Reach Solar, says solar and storage is already cheaper than gas and will be “well below” $100/MWh – the current level of wholesale prices – within a few years.
It is not really possible to say what nuclear power might cost in Australia, as we dont have any nuclear power generators, and they are talking about using Gen 4 reactors, which are rather thin on the ground... last I read only a handful in existence, and only a couple have actually produced power for a grid. Nuclear power is certainly not cheap, and along with all the risks, end-of-life clean-up cost (no doubt to be paid by the taxpayer), it really is a non-starter when renewables are so abundant and inexpensive, and becoming even less expensive over time.
The graphs presented in this article give an indication of where prices are headed, although it is for the US
Of note is that utility scale solar contracts are being written for $US21/MWh now in Chile.