Got these: From Ontario, not entirely sure, about 15 cars? Maybe 20?
Usually closer to the date, someone like Mark, picks some spots, and announces times, if you'd like to join the caravan down.
The Shootout event itself, has a park entry fee, that is different if you're racing (what, about $40?) vs. $10 for spectators. (going from memory)

Other years have counted 400 cars, or more.

Hope that helps... anyone else, feel free to adjust/correct, this is just off the top of my head.

I'm also curios about how much people have spent on gas in the past. Accomodations are easy enough to figure out, I've just never taken my car that far before.

Easiest way to calculate fuel Milage is to run mapquest from your location to Huron Ohio, and then compare the distance to the fuel milage you usualy get on the highway. Also factor in that if you join the caravan yo will get better milage as we end up travelling at a slower pace than the average DSM'er on the highway, as we usually have a couple of trailered cars travelling in the group.
Also when budgeting a couple of us end up going to Cedar Point, this has already been discussed as a potential activity for the saturday afternoon/eve.

It took me roughly one full tank of gas to drive from Ingersoll, to Huron (through detroit) and around norwalk/sandusky most of the weekend. Then one tank of gas to get home.

OK, Mapquest shows us going to Detroit area to cross over to the states following the North side of Lake Erie. Are we not crossing through Niagara Falls and following Lake Erie to Norwalk?

It really depends where you're coming from/who your going with. Depending on your location, like myself, Detroit way will be faster/shorter, but the roads through Detroit aren't exactly the greatest.