@aj @spacelizard - I'm going to second AJ. Go for refurb. Most anything will run Linux these days. I'm partial to used Dells, myself. But pick what you like.
Refurb doesnt put money into the pockets of techbros. Used machines are more sustainable than anything new, even newly built "repairable" machines - as no extra or new energy and parts are expended to make it.
For parts, you'd just buy another used model of the same type and frankenstein it. So go for something popular and common if you like.
Moore's Law basically no longer applies to laptops in any meaningful way. So laptops in the last five years (or longer) are still really great with modern linux os's.
Yay, #permacomputing!