I saw that Optus is selling the Xperia M4 Aqua for $229 delivered. The phone is locked to Optus. Unlocked versions are still going for around $350 on Mobileciti/$299 at Officeworks (white), so even with unlocking this is a good deal for Australian stock.
Features:
4G
8GB internal memory
SD card support
5" HD display
13MP rear camera
5MP front camera
2400mAh battery
Water resistant to 1.5m
I think you would struggle with 8GB of internal memory but if you don't use many apps, it could be doable.