Join PCA and go to the next autocross event. It's cheap and you learn A LOT about how your car handles in extreme conditions.
DE is a little more expensive and probably quite a lot more fun.
After doing these things for a while, I would think that organized, professional training would be worthwhile. In the meantime, just ask for an instructor when you are at PCA autocross or DE events. Instructors are available.
BTW, they say it is an illuminating experience to ride with an instructor who is driving your car on a track.
