PCA Carolinas Region does not extend to Charleston, but it hosts some DE, Club Racing and A/X events. They seem pretty active and have relationship with local BMW club.
I'm in Hurricane Region, so not soliciting membership. Carolinas events
are reasonably close to you.
PCA allows you to pick your region or to have dual membership if your geographic assignment is not to your taste.
If you want to check it out:
http://www.carolinas-pca.com/