We did dance class at a rec center. They also offer gymnastics and archery. Some have singing/acting/drama/art classes. We found our Girl Scout troop through school. We're lucky that our school has a good amount of extracurriculars, so all are through there now.

As a single mom, I just tried to find the most affordable version of what it was she wanted to do. I used Google and asked on Facebook (both my own network and in neighborhood groups).