I've been to a Skip Barber 1 day race school at Laguna, Bragg-Smith 3 day school at spring mountain, and Jim Russell Advanced 3 day course at Sears. I would have to say by far the most fun and bang for the buck was the Bragg-Smith 3 day corvette school, Excellent seat time, very reasonable price, great instruction and an amazing track!
Second place has to be the Skip Barber program, I only took an intro class but it had really good instruction and it was a lot of fun, I would like to go back for an advanced 2 day sometime... The Russell school I took was the advanced not the regular 3 day,,, it was good but to tell you the truth I can't give them a very good review. Instructors were only,,, okay and sales staff were kind of pricks!
I assume that everyone on here has some good experience so I would definetly recommend an "advanced" school, the regular 3-4 day programs are meant to teach someone that has little experience, although they are still a ton of fun.
The Bragg-Smith course is under new ownership,,,
http://www.springmountainmotorsports.com/ but I hear the same instructors stayed on and the course is still really good. Their advanced 2 day is $1900 and their standard 3 day is $2350. I would totally inquire with them,,, you might even be able to switch between C6 Z51's and C5 ZO6's. If you want a more extreme course they also have a radical(the car) school, not sure about the cost.