Lets see,
My Home region autocross, Ozark Mountain Region.
$20 for 5(usually) runs about 50 sec per run, we will round up to a min for coasting back to the pits
So its about $4 a min
St Louis Region, more open faster course, slightly more fun, but waaaayy too many people.
$20 for 3 runs, same low 50s runs, $6.67 per min, ripoff for sure
Kansas City Region, faster more open courses like stl, far less people.
$20 for 5 runs = $4 a min, but this region has a great option where you can run heat one, work 2 heats, pay an extra $5 and then run in another heat, so with that track time comes to $2.50 per min
All of this is with SCCA membership, as you can see, I like to go to the KC region whenever possible
I have yet to try track days, but as I see it, you may pay less per min on your car for track time, but there is more wear to the tires and brakes at those speeds, so that adds up to the cost.
-Matt