These DIY shops used to be really popular in the 70s and 80s. Especially on military bases. But most/all of them closed down. Before I would undertake a business venture like this, I would do my research and really understand why they went away. I've been told insurance became outrageous and cost prohibitive. But I don't know that for a fact. Unfortunately, nowadays I could see how an insurance company could be leery of insuring a company that loans lifts, power tools and welders to the untrained general public.
You also might want to look into non-profit club versus a for profit corporation because there might be better options. See if you can get ahold of the guys at Spannerland
near NYC, they have been having success for years. I think they are more club based though. Anyway, one of the founders of Spannerland, Mr. Cosentino is an inmate on this site. Good luck!
PS. I'd prefer a machine shop more than a garage. If I had metal lathe, mill or a table plasma cutter I could upload my Pro/E drawings to that and have brackets made up for my bike projects! That would be huge!
PPS. Check out The Crucible
in Oakland, CA. A fellow inmate turned me on to that place. Really cool machine shop and metal art fabrication facility. They have metal fabrication tools available for use by student members.