Clubs mostly, generally the vast majority of Makerspaces' income is solely the membership dues. There are a handful that are run more like businesses. Techshop is one and there's non profits like The Geek Group up in Michigan which has full time employees and a goal of each department/lab paying for it's own existence. Probably more but those are the ones I know of.

Usually you pay membership fees in exchange for access to the tools and stuff.