The cost depends on, of course, what kind of equipment you want, what clientele you seek and location, among other things. These are all related.
As a former gym owner, I can emphatically state that if you want to keep your doors open, you MUST have quality cardio equipment and plenty of it. This will be a huge draw to your business whether the members want to lift weights or not. This will also be a huge up front cost.
You might want to install a few tv’s in the cardio section. The hardcore spit-in-the-floor type gyms (my preference) such as the one in the animal-pak ads, have pretty much gone the way of the dinosaurs. There are a few still around but they’re the exceptions.
If your interests lean toward the fitness crowd then I would suggest selectorized machines such as Icarian (read:expensive). These folks generally just want to come in, do their cardio and maybe go through a training circuit without having to change plates. They don’t really want to pull 45 lb. plates off a bar that were left by the previous lifter or train next to big, sweaty, intimidating guys.
You’ll need mirrors and carpeting or mats on the floor. Equipment color should probably be white, to give the place a “clean” appearance. On the other hand, if you’re more interested in the bodybuilding/powerlifting crowd, equipment should be much cheaper. You’ll still need the cardio and some machines.
There is a thread somewhere here at T-Nation where a guy spent, I think, about $13,000 on equipment at Elite Fitness for home use. What he listed was better than most gyms I’ve been to. You’d probably want to double up on some of the pieces such as benches, bars, etc.
Depending on the size of your gym, I’d suggest at least 2000 lbs. of plates, probably more. That’s not including DB’s. I have over 1000 lbs. in my garage gym and am glad for the extra weight. Not including cardio, I’d estimate $20,000 to $25,000, maybe more, to have a commercial setup such as this. I built a lot of my equipment and everyone thought it was commercially built.
You can save yourself a lot of money this way. Ideally, if you could manage to combine the two crowds, you’d have a much better chance of success. In my opinion, the best way to accomplish this is to have a hardcore/freeweight area off to itself, if room allows.
Other things to consider are insurance, staffing, bookkeeping, child care, personal training and maybe 24 hr. access. You should plan on devoting a lot of time to your endeavor . If you just want a good place to train, consider pooling your resources with about 10 other guys and perhaps rent a building for your own private gym. There’s an article on this very thing at EliteFTS.com. A business course would definitely be helpful.
Sorry for not giving you exact estimates but once you know what you want, costs will be easier to figure. Maybe other gym owners can give you more input. I’m sure I’ve forgotten something so feel free to PM me.