Yep! I have an old work station computer that I built for a job years ago that I just transplanted into a cheep server rack case. Old hard drives from laptops as the main OS drives, a cheap networking card and switches. As the old laptop drives go out I'll just replace them with an SSD, it's a mirror array, so it's easy for one to go down and I just drop the new one in and have it all copy over.

An old Core i3 or Ryzen 3, 4+ gb of RAM, throw a cheap 3.5" HDD in it and install your OS. Proxmox is pretty preferred in the hobbyist scene, takes some technical skill but there's a lot of help out there for free on different forums. Feel free to DM me with questions if you like too! I'm not super reliable, but I'll try.