$80k is not a bad salary and I struggle to think of any Australian dev salary that is close to $400k.
Additionally, with good leadership 10 x $80k would almost certainly outperform 2 x $400k developers.
Additionally, with good leadership 10 x $80k would almost certainly outperform 2 x $400k developers.
There are lots of complex failure modes in a system like this, and minimizing them is an advanced skill. The learning curve for a competent generalist senior engineer to get good at these kinds of problems is significant. Designing and implementing a national securities exchange is a big deal.
This is a place where you want either experienced developers who have worked on other stock exchanges, or at least FAANG engineers who've worked on systems with analogous challenges. This is not a place you want to skimp on salary.
Of course OP thinks that $80k is a good salary for a developer so that ought to tell you how competent she is.