We don't really provide support for supportsystem.com here on the forums (since none of us have access to it).
The cost depends on how many agents you have.
https://supportsystem.com/pricing/
According to Google
$9 USD is 11.97 AUD
$12 USD is $15.95 AUD
$16 USD is $21.28 AUD
I do not think that you would be able to customize the back end, but you would really need to contact support to make sure that I am correct.