Not that cheap, I use too much data.
Currently on a 12 month prepaid deal through Kogan Mobile, $254.30 for 365 days, unlimited national calls/texts and 16GB of data per each 30 day period. It's kinda pointless to have so much data as I would have been quite comfortable with the next tier down, but it was barely any cheaper so whatever. Honestly below $30 per month I'm not too fussed about getting it too much cheaper.
Internet is $59.99 per month. I could save a bit by changing providers, but I'd need to sign a new contract (and I'm not keen on that). I have considered ditching the ADSL and going for mobile broadband only (at a similar price or slightly lower), but mobile data speeds aren't that great where I live.