Royalist:
1. Do the RAAF have the tanking assets to deploy A-10's to where you need them to be?
2. How does the RAAF get ahold of the tech data, fixtures, tooling, and spares to keep an A-10 fleet alive and well?
3. Pursuant question 2, how big of an A-10 fleet do you envision as meeting RAAF needs? That answer to that informs how much overhead is represented in establishing the support structure to keep an old (albeit wonderful) aircraft flying into the future.
4. That the F-35 is very expensive, and not getting any cheaper, is not in dispute. What is in question is: what are options, what is to be done about it ... and how do you support and maintain your fleet of whatever for a few decades?
With the F-35, at least, I'd make a wager that spares and maintenance support will be more readily available. For a price, of course.