Just how much do track days actually cost?

Recently I was posting about my track time at Thunderhill on facebook, and a man exasperatingly wondered how I could possibly afford to do so many track days a year at nearly $4000 a day in cost. I chuckled at what must have been a typo, but the gentleman was indeed serious, and seriously misinformed. Myself and another individual corrected them politely, but it got me thinking? Just what are my track day costs, ballpark? So I crunched some numbers on the C5 Corvette and the NC Miata and here's what I've got:

(If you're having trouble reading the above click to open the image directly)

So there isn't exactly anything newsworthy in there, but it does confirm something I already knew: The NC Miata costs significantly less to operate per track day than the C5 Corvette! Infact, it's to the tune of pretty much 3 times cheaper to take out on the track with the C5 Corvete costing $227, and the NC Miata costing $76.