IMO ebay seller protection no longer applies.   In the first transaction, you sent the item to the correct address.   It is not your fault they weren't there.

This is a new transaction, nothing to do with ebay.   I would send it with insurance through Aust Post as PJ suggest ^^^

We should not get caught up in the ebay seller protection thing that we lose sight of the objective.    The buyer has paid, still wants the item, has let you know his/her new address, and is probably open to paying more for new postage.