Amber,
Getting feedback from residents are good, but those that do respond they are speaking for themselves. When your equipment is broken and or outdated the replacement costs?
Now understand I am not trying to talk you out of it, but in going into any initiative I do analysis to ensure it is the right way to go. So, you know what your current costs are to get them to the local fitness center. It may be time to renegotiate for a better pricing. I always go in with the thought with those I am negotiating with is some money is better than zero money. The more members you have attending the better the bargaining.
When you purchase the equipment, then you need to ensure you let your insurance company know. Will this raise your monthly insurance costs? If someone gets hurt and it is determined that the equipment was not maintained correctly, or not installed correctly then you have a situation. People come in use the equipment and they sweat and normally will either leave it or brush it a couple of times with a towel and that is it. How will you ensure the place stays sanitized and your tenants do not pick up some kind of infection?
Then, the big question is why do you want the gym, and how do you know you will receive the proper ROI? What if you see that you are not, and then what action will you take?