Here at Harris Hill Raceway in San Marcos, Texas, you can ride as a guest for $150 per day.
To become a member costs you a one time $500 entry fee, of which $150 is deducted if you've previously done a track day, from then on it's only $150/month
We just did a RideSmart day at COTA which cost me $400 for the day, plus another $75 for a garage spot.