Up in the Northeast the tracks tend to be sold out. Watkins Glen was sold out at $14K/day a couple of years ago (see here for what the 2014 schedule looks like at a top-line track:
http://www.theglen.com/~/media/6BF8F...BDF07D6ED.ashx).
Mosport, which I consider to be the greatest track in the Northeast, was $6K/day a couple of years ago. Stupid cheap, especially if you think about how many cars you can put on a long, fast track like that and still not have trains in the slow groups.