Said in another comment, my server averages around 100-200W. It's equivalent to running a gaming PC.
The reason there's a lot of cheap servers on eBay is that their support contracts expired and are absolutely ridiculously expensive to maintain for a big company. It's easier to get a new server (which will likely have performance and efficiency upgrades as well) than to continue maintaining a server that no longer has a support contract.
The reason there's not many servers in people's hands is size and noise. Servers aren't meant to go in a house; most people don't have server racks in their home. And by default, the fans are jet engines, even behind closed doors.