Recently I picked up a $100 Lenovo ThinkCentre M710Q off ebay with an i5 7400T, 8GB of ram and a 256GB NVMe SSD to add to my Proxmox cluster.
The good & Bad
Mini PCs are built to be small, quiet and power efficient, perfect for a home server. They’re also tiny, hence the name meaning they can live pretty much anywhere.
However, their form factor makes them hard to upgrade for future expandability and hard to add redundant storage to.