Seems the extra cost is about $20,000 per pilot based in Broome.
Bend alot, you have left out the housing costs and most of the perks. 7-10 houses would have to be provided to the 7-10 extra staff that would occupy Broome. How much would it cost the RFDS per house, per year? Some may be rentals, some may be purchased. And the perks for the nurses and doctors? The doctors are on hefty salaries and receive hefty perks to match.
Stabilisation was in Darwin not Kunnanara.
You're basing that on the statement from the RFDS. Every statement from them should be taken with a grain of salt. It comes down to what degree of stabilisation. A certain amount of that stabilisation would had to have occurred at the Kununurra hosital.
This real example shows your Perth only jet base as a massive time delay over Broome, as the PC24 would fly direct into Kunnanarra (no feeder PC12)...
You're assuming that the RFDS only became aware of these cases when they first arrived in Kununurra - and that on arrival in Kununurra, they were ready to instantly go to Darwin.
In reality, the RFDS would have been aware of them hours before they got to Kununurra. And they would have spent several hours in the Kununurra hospital, on top of that. Plenty of time to get the jet up from Perth.