Corsair K95 Platinum XT with Cherry MX Brown switch for $231.61 from Amazon AU (delivered by Amazon US). If you want your co-workers/family to hate you the Cherry MX Blue is also available for $241.81.
I've never seen this keyboard this cheap and searching OzBargain didn't reveal any previous sales, so this could be the cheapest ever. Note this is the upgraded XT model, which has:
- A leather wrist rest (instead of rubber);
- PBT keycaps (instead of ABS);
- 5 onboard RGB profiles in memory (instead of 3);
- Compatibility with Elgato Stream Deck software if you need it (still compatible even if you don't need it).
Shipping is free with Prime but comes from the US so may take some time. Amazon lists the model number as "CH-9127412-NA" which seems to be the standard model sold by Australian retailers.
Obligatory "this is my first post so I apologise for mistakes" disclaimer.