I know that I can run PCF Dev on a single VM. But I have a few old PCs that aren't doing anything. It looks like PCF needs to run on VMs provided by AWS, Azure, Google, OpenStack, or VMware. So maybe I would need to install something like OpenStack on my PCs first - perhaps with Ubuntu/MAAS/Juju?
This is the only bare-metal type solution I've seen for Bosh -> https://www.cloudfoundry.org/bosh-rackhd-cpi-running-cloud-foundry-on-bare-metal-with-bosh-2/. Otherwise, you're going to need one of the virtualization layers supported by a Bosh CPI.
The next step up from PCF Dev would probably be Bosh Lite. Beyond that, perhaps try the Virtualbox CPI? Both should run on a single server or laptop.