So Spank has done the ultimate guide to getting a car to the track cheaply but he has skills and experience beyond almost all new teams. So break it down into what you have to do to get on track...
At least one teammate, preferably 6...that way you have a chance in Hades of getting to the track with two teammates. Cars are "easy" by comparison to people. Make sure everyone understands the overall cost...just tell them it is $1500 each to get to the first race as it is decent round number.
Car $300-1500. Amazingly, some cars can recoup their purchase price in selling non racing related items in a part out. It is a time verses money thing.
Cage $750-3500. This is a super important item that has to be done right both for your safety and to pass tech...without which you do not race.
Seat, fire system, kill switch, etc $900-one gazillion. Low end is finding a used seat, minimum price fire system, $25 kill switch, etc. More realistic is $1500-2000.
Fuel, tires, brakes $200-$6000. Small 4-cylinders burn 4-5 gallons an hour while a Viper V10 close to 10 gallons per hour. Tires can be the mismatched 7 year old all seasons that came on the car or $175/tire on a $300 wheel x 8. Brakes can be servicing what you have, getting nice street pads/shoes (including spares you can return) or a full Wilwood setup...best option for a new team is excellent front race pads on new rotors with racing DOT 4 brake fluid.
Others mentioned renting racing gear but most of my teammates have taken the other tack...buy your gear with the understanding that if you hate racing you can get $0.50 on the dollar selling it after one race which, with the exception of the HNR, is break even with a single weekend of racing.
Do not forget how you will get it to and from the track, gas cans, shade, food, fluids, therapy bills, divorce, etc.