Well, I don't really, but it is something I have wondered before.
Let's say I wanted to practice car racing as a hobby. I don't mean being truly competitive in any series, but still a relatively serious hobby. I would already have a cetrain minimum of skills needed to drive, but I would want to develop my racing skills and improve my personal performance - pretty much like a dedicated hobbyist in any other sport. Assume that the driving is done on some kind of track and street legality is not a concern. Other than that I don't want narrow down the type of car.
Assume that I have a respectable disposable income but no fabulous riches. What would be an entry-level racing car that allows "real" racing but keeps cost (both purchase and maintenance) within somewhat reasonable limits.