I've had good luck with 7000 series Dell Precision Workstations. They are built like tanks, hold seven drives, have 1000W+ power supplies and are cheap (from reputable sellers on eBay in the US, don't know about Australia). The processors are Xeons and the PCI slots abundant. The 7400 I bought new is ten years old this month. It has spent about eight of those years on. It's been through Windows XP Professional x64, Windows 7, Windows 8, Windows 10, and about half a dozen Linux distros (currently Ubuntu 16.04).
Anyway, the 7000 series are beasts but don't run as hot or loud as a rack server. They are big, expandable, support ECC RAM, and include things like parallel and serial ports in addition to USB.