UPS battery backups have been popular at OzBargain lately and Centre Com have this one on clearance with free delivery.
The downside for some people is that it only has C13 plug outputs, but it does come with two C13-to-C14 cables and C14 to AU plugs can be purchased for <$5 online. For me personally it's not a big deal as I run a homelab and can run servers and NAS drives off them.
There's also a 850VA 480W for $69 and 650VA 260W for $49, however they're instore only.
Protects equipment against blackouts, brownouts, overvoltages, surges and line noise
AVR battery backup allows time to save files and safely shut down during blackouts
8 C13 outlets provide power to PC, home theater or digital signage equipment
Easy-to-read LCD touchscreen provides valuable voltage, load and battery data
High >95% efficiency with low BTU ratings saves power and lowers your energy costs
I don't see any energy specs, so battery not included?
Can I use a 12v deep cycle car battery?