Scda1.com, pdadrivingschool.com, trackmasters.com
These associations all share the same principal. Pay as you go.
Most of the time they cover tracks like Lime Rock, Millville tracks, Watkins Glen, VIR.
Check the websites for their schedule, most of them will have it by now.
SCDA highly recommended. I did 15 day total trackdays in '08.