Ryzen 9 5900X CPU for $565.39 which AFAIK is the lowest price in Australia so far. Remember to select the "free shipping for over $39" option during checkout.
AMD is due to release their new AM5 platform later this year which will offer superior performance. However, increased product complexity, supply chain issues, falling Aussie dollar, expensive DDR5 RAM and runaway inflation will mean that the new stuff will cost a lot more. Therefore, I think that it's still worthwhile investing in the mature AM4 platform, especially if you already got a compatible motherboard.
The 5900X has been slightly cheaper before via Shopping Express but for Amazon it's a new low.
Interesting also that this CPU has the best cores/$$ ratio in the Ryzen stack right now with the exception of the 5500/5600G