It’s not that hard to start racing but it's much harder to develop sustainable racing. There are many pitfalls along the way and one of the biggest is building your own car to start. I got some good advice when I started (like what Jake and Kirk said above) and for once I listened. The biggest thing people don’t understand is that it’s not about the car. The car is completely irrelevant. It is a box with wheels. Racing is about driving and what you want to do is find a way to affordably and reliably drive a box with wheels on the track. It’s tough because people get into racing because they are “car guys”so naturally they are focused on the car.
When I started I wanted a spec miata. I bought an ITB Pinto “just to do my driver’s school in”, and ended up racing the Pinto for 4-5 years now. If you would have told me when I started that I’d be racing a Pinto… uh, no. Just as an example, my brother’s Pinto is for sale in the classifieds. Ignore the fact that it’s a Pinto (I know) and take a look at what you get for 2800 bucks. And there are many other good deals out there.