You have a gym onsite at a corporate location and you are charging membership dues? Is it open only to corporate employees or also to the public? The corporations where I’ve had access to a gym on-site (two) and where my husband has had a gym onsite (one) have been free and funded by the parent corporation, including the group-ex staff. Only personal training cost extra.
Consider talking to work groups. For example, I recently did a 10 minute revitalizing stretch and breathe session for an executive team that was meeting all day. If you can get that 10 minutes at the end of a lunch break during a long day of meetings, you can help people feel better and show them very quickly how effective tuning into their bodies mid-day can be for alertness, concentration, temperament, and alleviating pain. After they’ve seen you a couple of times, they might venture to your facility to see what else you can do for them.