Purchasing more Hobart AWD’s is not really feasible because a lot of the systems are obsolete, especially the drivetrain. The RAN would end up with a Mark II AWD without much commonality for maintenance and logistics. The Navantia hulls are also quite small with the systems jammed in, thus making maintenance more difficult and expensive.
All the latest information indicates that the Type 26 hull is the most suitable for RAN requirements despite the furore about the selection process. The very quiet drivetrain is part of the reason for the high cost but that is why it makes such a good ASW platform. The hull size allows much more flexibility with system installation and future growth as new technologies enter service.
The Hunter class is being developed with all the sensors of an AWD but will have a smaller missile capacity due to its ASW role. The BAES proposed 96 cell Type 26/Hunter variant offers a much superior AWD to the Hobart class due to better sensors and twice the missile capacity. It would be a vessel that would be upgradable throughout its service life and remain fully capable in the modern sensor environment and, it would have a large amount of commonality with the ASW version thus reducing logistics and maintenance costs for the RAN.
IMHO, acquiring more Hobarts is sticking with technology that is already starting to become obsolete whereas the Type 26/Hunter is the future - there are signs that the USN agrees as they are totally rejigging the Constellation class in an attempt to have similar capability.