Man, I wish you'd posted this a month ago when I was still in Greenville for work! Folger Subaru held another Subaru Showdown-type event at Carolina Motorsports Park (2 hours from Greenville, in Kershaw, SC). $135 with an instructor, $125 without. They held a track day on the East course and AX on the west course (AX was much cheaper).
I highly recommend some AX experience before track time, as you'll get used to lower-speed extreme maneuvers, but you'll be fine with an instructor the first time on a road course.
As far as organizations, PCA is a good one. I have a friend with an NSX and his dad with a GT2 that run with them at Road Atlanta and other tracks. Also, there's Tracks Unlimited, www.tracksunlimited.net
(also search for them on FB, they have a group page there). Good group I've run with twice and has solid instructors (including one with a 07 WRX wagon, a good friend of mine). If you have access to the latest Grassroots Motorsports, there's an article in there geared torwards getting out on track and organizations to drive with. Track Guys (www.trackguys.com
) is also holding their first event at Barber Motorsports Park in Birmingham, AL. Worth the drive, great track and facility!