What about this argument?
Given
1) s9A does not mean that safety is the only consideration
2) CASA policies (shadowing ICAO) say that risks should be kept 'As Low as Reasonably Practicable' (also see s11 - international agreements)
3) Policies that are not in conflict with legislation are relevant for the interpretation
Then doesnt this mean that ALARP is already a consideration for decision making? (Or, if it isn't, then a court may find that it should be...)
And terms like 'reasonable' are very established legal concepts... Cost is very much a test of 'reasonableness'
It also occurred to me that the ATO has quite well established rules thanks to the 20 odd million taxpayers (some of whom are quite litigious) who are constantly testing the system. Contrast with the 2000 odd AOC, AMO, aerodromes etc, none of whom want a bar of dealing with CASA.