Here are a few ideas:
-Create a team or teams that will participate in an obstacle race and then create a training program that will help the members to prepare for the race. Free membership (for a period of time) for those who will sign-up to train for the race.
-Sponsor and/or create a race event. If it goes well it could become an annual event with a tremendous exposure for the gym.
-Offer corporate rates for local companies and their employees.
-Seek and bring in some of the best trainers in the area, even if it costs a bit more. This will attract some positive attention.
-Contract with local high schools or police/fire departments that don’t have the facilities (or space) for their students or members to train.
I hope this helps.