You'll never get anything of that scale off the ground in Hillsborough County. The municipalities will never allow the needed zoning and the taxes will eat you alive.

Personally I would look into farmland in Pasco or Polk County. Even then you'll need a plot that has zero neighbors within a one to two mile radius or else you'll spend several hundred thousand dollars in the future for earthen berms around the place to deaden and redirect sound.

The idea of "come & play" individual rental track time needs to be re-thought, too. You'd be better off building a big asphalt pad and having the autocross and drift clubs rent it and run with their own insurance. There's the possibility that karting organizations would rent it, too. But leave out any open tracking ideas. They have enough established places to play. Realistically you couldn't expect more than $2,500 worth of rentals per month, on average. Car manufacurers spend good money on sites for "ride & drives", but they'll want a place with some permanant facilities with a/c for classroom training and such. And their promaotional events need to be in more accessible urban areas.

I've discussed this with some well-to-do entreprenuers and cautious estimates w/o any facilities, sewer lines, drainage, electricity, or fencing, came in somewhere between $600,000 to $900,000. My former boss, Carl Lindell, spent the better part of the last 35 years developing land in the Bay Area. He said we'd be better off developing an ATV/4wd park where improvements would cost $0. Property taxes in Pasco would run about $11,000 to $15,000 per year for a plot of suitable size. $2,500 per mo. X 12= just paying the taxes and never recouping any of the investment at all. And then in eight to ten years you'd have to spend another $300,000 to get it resurfaced (if you varied the drift courses enough that they didn't tear the shit out of it even quicker).

Don't give yourself any more brain damage on the subject. The best you can hope for is a whole lot of roll-over's for the lottery and you hitting it....maybe then we'll see an FIA spec road course with a paved infield for autocross...