Thanks for the information everyone.
I spoke to someone at Westpac (in Australia), and yes it is correct they do not have any alliance partners in Indonesia.
So it would be a $5 fee plus 3% conversion rate, for a debit mastercard.
I also spoke to someone at the Commonwealth bank, and they said there is a $3.50 charge for using their atms in Indonesia plus the 3% conversion.
She then suggested something called the Travel Card which sounded very good. You pay $15 for the card, and the first top up on the card is FREE, then 1% thereafter for top ups.
There is NO fees at all apart from the conversion rate of 3%. Sounds perfect as I only want to take my own money as back up.
So hope that helps anyone else out with the same confusion I had to start with.