Racing Circuits

I have a list of a few racing circuits located in California, http://www.racingcircuits.net/UnitedStates/ca/ but I was just wondering has anyone every scheduled a track day with just a few cars at any of these tracks and if so what expenses are involved and how was the experience on an actual track? Also, if someone can provide a more up-to-date list of circuit tracks around California, it would be greatly apprechiated.

Thanks in the mean time, looking forward to the replys.