I don't know about Australia, but in the US we can buy our own cable modems instead of having to rent from the ISP. I've tried the SB6141 and that was a pain to set up (had to call the cable co) and the one I got had a bug or something wrong with it to where it would not get the full speeds with a gigabit link to the router, I had to set it to 100TX half-duplex (really weird bug) for it to work correctly. I ended up trading it in for a Zoom 5341J that was able to set up through the browser instead of calling Comcast, and no weird link issues. Really the Surfboard probably works great too if you get a unit that isn't faulty.
Anyway I don't know if either of those are available in Australia or if your cable co doesn't allow you to use your own modem, but I thought I'd share my experiences with those in case it helps. BTW the Motorola was about $99 USD and the Zoom $69 USD, fwiw.
Yeah, like Freq said, unless Australia is different than the US, you can buy your own cable modem. It just needs to be compatible with your ISP's system. So first step, find out what modems are supported by your ISP (just google it, you can usually find a list or at least the requirements). Then you can figure out which to get.
Just to add to what has already been said; you need to find out what DOCSIS standard is supported by your ISP. For example my ISP supports DOCSIS 3.0. I use the Motorola Surfboard SB6141 and have had no issues.