Standard PC components mounted to a $20 rack-mount shelf. This is a project from about 3 years ago, when anything “Rackmount” was even more expensive than it is today (not that Rack PC’s are all that cheap now…). With a system board that has on-board Ethernet, and 1U power supply from ebay, this could easily be a $20 or $50 1U setup as well. Thanks Brian! Link.