There are a few places on the web to get people started with the process of getting an SCCA Regional License.
I would however like to share my own experience and "insights"....
While I was a "high performance driving" even instructor for a few years, I eventually got a little tired of driving my slightly modified street car (a 2003 3.0L BMW Z4) on the track. The problem was not that the car was not fun to drive, because it is. The problem was that the car is a bit heavy (3500 pounds) and while the engine has plenty of torque and enough horsepower, slowing this car down from 125mph to 40mph is no small feat for the front brakes. I have ran though too many brake pads, too many rotors, and too many front caliper rebuilt to count. As I was getting faster on the track, the cost of keeping this car running simply became prohibitive. And in the end, this money was spent to chase slightly faster lap times while providing none of the racing excitement I was getting karting at AllSports! I also made the mistake of seating in the passenger seat of a Spec Miata during one of the Friday At the Track (FATT) event and by the exit of Turn 1, I knew that Sharkie (my Z4) would never be that competitive. These short 4 laps driving a Spec Miata would prove to be quite the catalyst :-)
In late 2012, maybe prompted by some changes in my personal life, I decided that I had waited long enough, that one only lives once after all, and that I should just bite the bullet. After talking to many racing friends, I came to the conclusion that I might not want to buy my own race car but should instead try renting one, at least while I was taking the SCCA Racing School. This way, if I stunk at this or did not like it (Why would I ever think that to be a possibility...) I could just walk away...