I find that Microsoft Authorised Refurbishers are a good place to start to find cheap old corporate machines - eg I can typically get something like an Intel i5 8500T based Lenovo/Dell/HP mini PC with RAM and SSD for less than £200.

I actually bought a Lenovo M910Q with i5 6500T, 256GB SSD and 8GB of RAM for ~£100 in the last year.

It'll absolutely demolish a Pi 4 at CPU & GPU performance, can take much more RAM than a Pi, idles at <10W on 230V mains, you get the bonuses of easy software compatibility as it just runs any mainstream Linux distro & and it runs x86_64 code, it has real storage interfaces (SATA & NVMe), and has an Intel NIC.

For home server uses, they're really nice machines.

The keyword here is "cracked screens".