Was going to buy the US import deal on Amazon but did one more search on eBay and found this.
Another seller offering the same price - https://www.ebay.com.au/itm/AMD-AM4-Ryzen-9-3900X-Processor-...
(credit to users https://www.ozbargain.com.au/user/70605 & https://www.ozbargain.com.au/user/283109)
For those who bought it earlier today at $658.56, can try to claim the eBay Plus price protection - https://www.ebay.com.au/help/buying/paying-items/ebay-best-price-guarantee?id=4627
(contacted eBay CS and found that you can't claim best price guarantee against other sellers on eBay)