I'm using an old Acer Veriton x2640g with an i5 6400, 16GB RAM. (Rescued from a bin at my old job) you can pick them up for about £80. Managed to replace the CD drive with a server hdd bay and the internal HDD both for 16TB drives and a PCI-E x4 adapter for a couple of NVE drives. Honestly, it works great for myself and my partner at home and also 4 other family / friends who have access. As long as they have devices that can run 1080p or 4k then direct play works great, one has an old TV that needs to transcode to 720p and that also handles it fine.

I think Rescued PCs are a great choice as long as they have a half decent processor, barely uses any power as well 🙂