I would look into thin clients and Lenovo etc. tiny PC for office on eBay. I run old low power low noise rackmount Supermicros which are nice but hard to find at low prices.

Factor in power bills and heat and noise into your calculations.

I hear you, but Proxmox does a great many more things than just run containers. Admittedly, many selfhosters won’t need these.

It’s a NUC so sufficiently poweful. Proxmox isn’t fat by any means. If you run your stuff in containers then Proxmox (I aways install it on top of Debian) is your hypervisor is your base system. You typically don’t install stuff on your hypervisor, though I do some very select things.

Proxmox with Debian containers.

About 70 W for opnsense on a thin client, an Atom Proxmox and fanless 24 port switch. North of 6 kW if I fire up everything.