Was a driver the first year at CMP in Kershaw, SC and pitted the next year.
It's an absolute BLAST!!! We ran a Civic hatchback.
What I can say is the first year don't expect to win anything. Just go have fun. It's the 2nd and 3rd years (you can keep your previous years mods and add another $500) you'll really start seeing things happen. All said and done, it's well WELL worth the cost of admission.
Also, I can confirm a few questions on here:
It's true that safety items do NOT count towards the $500. So brakes, tires, seats, extinguisher, cage and so on.
Yes, the can and sometimes WILL take/buy your car for $500 if they deem fit. Or crush it, or let others beat it up, or weld on spikes pointed TOWARDS your own radiator... I've seen them even make an entire team wait a few laps while doing cadences in the pits. It's all in good times and spirits.
Oh, and Ebay parts here, those knock off, never fit parts for 3 and 5 dollars are winners. We ran ebay coilovers for $35 and had to prove to the judges where we got them from and what price. KEEP RECEIPTS!!!