Im prepping a car at the moment , im taking my time with it an doind all the work myself
it depends on how much u can actaully do yourself i think but as a rough estimate id work around these figure
Roll cage 300-400
Fire extinguisher 100-200
Race seat 200-300
Harnesses 100-150
Wheels 200-300
brake overhall 100-150
Tyres - There is a nominated supplier so im not sure how much these are at the moment
suspension 200-300
going at these prices and working on the assumption that the car is in good condition should get you on the grid , but remember that youll have to factor in your race licence , and personal safety equipment , IE helmet, race suit
of course you can spend alot more than that or sometimes buying a ready built car is often cheaper