I don’t know if there are any minis up on the site, but Apple has a refurb store that is usually pretty solid on price (or was last time I looked). Pawn shops aren’t a bad idea either - typically heavily marked down electronics, and if you find little ones tucked in next to bodegas you can find some unexpectedly good electronics.
I'm also curious to find out how it works for multiple users on a single computer.
edit: I also wonder what the cheapest mini i can get is. Probably some used market? Hmm