Cheap to buy old hardware, but electricity to run those old rigs isn't really cheap in many areas now. My server is costing me about $100/month in electricity costs.
replyIt does have 16 spinning disks in it, so I accept that I pay for the energy to keep them spinning 24/7, but I like the redundancy of RAID10, and I have two 8-disk arrays in the machine. And a Ryzen-7 5700G, 10gbit NIC, 16 port RAID card, and 96GB of RAM.
It depends on the type of hardware that you use for your server. If it's really server grade you're totally right. For example cheap memory+CPU+MB x99 off AliExpress are cheap but they're not very efficient.
replyIn my case I fell in love with the tiny/mini/micros and have a refurbish Lenovo m710q running 24/7 and only using 5W when idling. I know it doesn't support ECC memory or more than 8 threads, but for my use case is more than enough