I know the roll cage is probably the the single most expensive purchase to go racing, but after that it's all down hill....
Once the cage is in and you have the other safety items installed, you can go racing. To grater belief you don't need to have the car as fast as she can be or have new race rubber or the latest "go fast bits" ect..ect.. JUST GO RACING. Half the thrill is actually being out there and giving it a go. Learn the craft, become a better driver, have a s%#t load of fun and then... When time and budget permits, take the next step.
Life is too short! I have stuff all money to go racing, so does Briggsie, Perry, Maxfeild..... The list goes on. You simply don't need a V8 SUPERCAR budget to live the dream.
JUST DO IT! While you're still living and breathing.....