Go through your results for flights to Coolangata in Australia with Netflights. Although Royal Brunei usually has the best prices, it's best to double check what's available for your travel dates.
If these flights are too expensive, try searching for a different time of year. So if your dates are flexible, consider looking at different times of year.
So, if the flights to Coolangata don't work for you, you could always try searching for flights to other airports in Australia.
For even more options, check what other airports you could fly to Coolangata from. You might be able to make a saving by going from a different airport or city.