Lulz. You would want to find a decent car, spend around $5k to get it ready to race (cage, seat, brakes, wheels, tires, 5- or 6-point harness, body/window modifications, tow points, gutting the interior, replacing any bad components, driver/pit radios, etc), $1k to register it, $400+ in drivers fees, get a tow vehicle to get the car there and back, gather up a whole set of tools, fluids, and spare parts to bring to the track, buy fueling equipment (we bring 2x55gallon drums and 6x5gallon filler tanks for two cars), on top of $1,500-3k in personal safety gear (helmet, head sock, suit, gloves, socks, shoes, and head restraint) on a race series you might not even like?
You might think that you want to build a car for it, but you should really drive with another team before building a car of your own. Dip your toe in the pool of crazy before jumping in head-first.