The Caterhams are available thru Autocourse Inc. All you have to do is show up and drive. They buy the gas, tires, beer, everything. The current hit is $500 for the weekend. You pay for your own entry fee. If you bring a buddy, they knock $100 off. Don't quote me, though. Things are subject to change. I had a blast, and it was way cheaper than bringing my own car.
Tell them I sent you. Here is the contact info. Ask for Will or Virginia.
william@autocourseinc.com
949-499-3122