The costs associated with being a weekend warrior on the race track come down to how competitive you want to be. Maintaining a car in racing trim has some costs over and above what we experience with daily drivers.
If you have a car that is rare and hard to get parts for that creates money issues all by itself.
But, if you want to get an old beater sports car and get it race-ready and go have fun in local club racing or even SCCA events, it doesn't have to break your piggy bank.
My first driving instructor had an E production 356. I can't remember if it was a speedster or a roadster, but it was green and had a big roll cage and he had been campaigning in it, at that time, for ten years. I asked him if he was rich, independantly wealthy, or what, I mean he had his own trailer and everything, and he just laughed, telling me he was about to ask me the same thing regarding my race car du jour!
To guys having fun.