I have a old optiplex 7010 with i7 and 8gig RAM. About 70€ on eBay. I upgraded it with a nvme SSD to bolt from (great tutorial here) and salvaged an old SATA HDD from an external case

Currently runs 11+ container in proxmox without issues. Way beefier than a raspberry pi. I also have room for 3 more hdds to put in a mergerfs system and 2 additional pcie slots für things like a faster LAN card or an additional SATA controller