Only if you are looking for a latest-gen or last gen machine. You can find some old NUCs for cheap, and there are lots of mini PCs or thin clients for around ~100. Yes about twice as expensive but more than twice as powerful (in both processor speed and features). Of course only if you plan to use it as a Linux computer, not for GPIO stuff.
This isn't super-practical for a commercial application which requires 70 identical machines.
Not only are they expensive and relatively large, machines that have had previous owners often have mystery issues which make them great for home tinkering projects, less so for something that can get you in trouble if it breaks down.
There's a reason companies buy new parts instead of employing teams to scour Craigslist for deals.
