As I wrote in the "Comments" section of Kym Bergmann's fine APDR article of August 22, 2023, I would say Australia and other potential HIMARS customers are being asked by the US to pay hugely inflated prices to CROSS-SUBSIDISE THE HIMARS THE US IS GIFTING TO UKRAINE.
In support of this Ukraine has about 50 HIMARS systems [1] that would have fired about 15,000 HIMARS rockets since February 2022 [2].
The US would be frustrated Australia has "only" been sending Bushmasters to Ukraine and sending Australian trainers to the UK to train Ukrainian Army recruits.
In view of that raising the price of US weapons amounts to a useful UNDECLARED WAY that Australia can fund US arms being given for free to Ukraine.
[2] https://en.wikipedia.org/wiki/M142_HIMARS#Ukraine "As of February 2023, CNN reported that Ukraine had expended approximately 9,500 HIMARS rockets" + an estimated 5,500 additional rockets for the additional 6 months to late August 2023.