I am the organizer for Seacoast Contra in Newfields New Hampshire. We are a small-town group with a big heart :)
I've boosted our dance with Facebook approximately 3 times. The budget I set was very low, as we're on a very tight budget ($15) We've polled new people how they found us...and we received no response from a Facebook ad. Most found us multiple ways, including signs we place near our dance a week before and a sandwich board outside the dance, referral from friends, posting on our FB page, email list and Meetup posts to multiple groups. Multi-faceted means of advertising our group has made it a viable dance. We just celebrated our one year Contraversary. Our group has grown steadily.
I do think there is value in boosting our group....it gets us noticed, and planting that seed is essential. I think that a bigger budget for a larger group would be a great way to get noticed and bring in new dancers It just can't be the only way.