I pay $150 a month for my 80GB plan and it's a good price. Sometimes usage goes up to 100GB and doesn't include "illegal downloads" but includes working from home, five PCs at home, iTunes downloads (including movies and TV episodes), online backups, MSDN downloads, etc.
Mauricio, have you considered that at the $150+ price point you could have two connections, Telecom Big Time and Telstra Cable 10GB?
A bit of trickery at the router/gateway and you can route stuff that's fast on Big Time via Big Time eg: general web, email, local traffic, youtube, msdn from akamai, itunes from akamai etc. Then route your voip and any international that is slow on Big Time via your Cable connection...
That would give you unlimited data for non time sensitive downloads and fast real time international for stuff that isn't that great on Big Time, for around the same price you're already paying!
I know a few heavy usage homes/flats going with 2 connections either Cable + Big Time or Maxnet Naked ADSL + Big Time ADSL. The best of both worlds once you're spending $150+ /month imo.