My go to for home servers for like 20 years has been used dell optiplexes. They are quite reliable, easy to find, pretty cheap, come in a few different standard physical sizes, and last a long time. The one thing they could do better at is energy efficiency. I spent a total of US $450 on the last two that I bought. I added an LSI HBA to one and it runs 4 HDDs in raidz1.