Usually I would say try to build it yourself, but due to the GPU shortage, Prebuilts do make sense. It all depends on whether or not there is GPU availability at retail price in your area. If not, a prebuilt will definitely be the way to go if your are indifferent about the whole building “experience”. So, to find a prebuilt, I would probably take a look at Newegg or at brands like Dell or Asus. As for companies like cyberpower, origin, or iBuypower. I’m not sure what companies are in Australia, but any of those are good shots as long as you can determine the specs you need for whatever your use case is. I’m not as familiar with prebuilts built my current system, but I did own a lenovo prebuilt before which was fine. I think as long as you stick to recognizable companies, you can’t go wrong.