I suggest that you look long and hard at this as it may not be best for you to settle in Vanuatu, especially if you have to head back to Oz for any major treatments.
Insurance premium costs are high. I live in South East Asia and cover for me, wife and 3 children is US$,12,800 a year and I have access to the best hospitals in Thailand.
The cost of premiums depends on what sort of cover you want. It ranges from basic hospital only, hospital and outpatients through to full medivac.
Insurance for you that covers medivac to Oz would be very expensive. I suggest you do a Google search regarding this.
You may also look at what medical facilities are available in Noumea,New Caledonia as somewhere to go to for treatments.