As a clickable link:
https://reneweconomy.com.au/wholesale-prices-surge-as-wind-and-solar-output-falls-to-zero-in-south-australia/amp/The Australian Energy Market Operator - AEMO - has a publicly accessible website where the power price horsetrading between the Eastern States is publicly visible all day long.
https://aemo.com.au/en/energy-systems/electricity/national-electricity-market-nem/data-nem/data-dashboard-nemSA usually has the highest prices, particularly outside solar generation hours, and they frequently import brown coal electricity from Victoria via the two interconnectors. TAS is often the cheapest, due to their hydro. Quite often these days power prices go negative in some States, which means black and brown coal generators, which are slow to turn off, have to actually pay the market to take their power, until they can disconnect some of their generation. Negative pricing is one of the main factors making base load power generation uneconomic in recent years, together with ageing equipment and higher coal prices.
If you look at it now and then, particularly in peak demand times, it is easy to see how volatile power prices can be. There is no doubt a lot of 'gaming' of pricing going on between renewables generation and others, in both directions.
WA is not in this trading system, because there is no power connection across the Nullarbor. WA has its own pricing system
There is a phone app with this Dashboard data also, but it is not as easy to read as the browser version.
(20min delay)