Buy a Yellow, Black, White or Red Lotus Esprit V8 SE. Do it up to around 580hp and it will beat many race cars if you know how to exploit it's rear weight bias. If you are someone who doesnt have the driving style that works with a rear weight bias car, then dont get it. Some people will never master these cars.
I would never buy a race car. They are easy to win, and way to expensive.
If you buy the Panoz, which is probably the worst race car in the game, for 2 million cr. I will laugh my ass off.
PS, if you like the Panoz and the GT40, you wont be able to drive the Esprit. The Esprit and RGT type cars are tuned for drivers with a completely opposite style than people who like to drive the GT40, Panoz.