There are x200's on ebay w/o OS's for a couple hundred bucks. This should be fun!
The Libreboot site lists supported hardware. You need a bios programming chip (cheap on Amazon). Freeing your bios is a dorky thing but valuable to learn. Here's a vid that'll give you a sense for it (Mental Outlaw is great) - https://www.youtube.com/watch?v=WyItt8FJWIs
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You get it. I have a big stack of ThinkPads.