Depending on where you are, there'll either be local auctions of surplus tech, or eBay / refurbishing stores selling these kinds of things. I always went for Dell Optiplex, but there are HP and Lenovo equivalents too
Yeah, we used to have Free Geek Vancouver here, but they unfortunately shut down recently.
Still, my intent is moreso, well, companies are literally throwing these systems into the trash, so paying for them feels like I am getting ripped off. I'm always hoping for the opportunity to snag a system or two that is being tossed. It has happened before, or I've paid like $5-10 for something that is destined for the dumpster. It definitely seems like a "have to be in the right place at the right time" kind of thing, though.