Um, even the skilled teams (as in fabrication geniuses) rarely rehome a cage and that is only when the shells are the same. The cage is a big deal. You reasonably have three options:
Buy a recently passed tech Lemons car (cheapest by far...$1500-3000 for a tech worthy car with spares)
Buy a pre-bent cage from Roll Cage Components (about $750 shipped) and have an expert welder install it $?
Pay for a full custom cage from a cage builder that will follow the rules in "How not to Fail Tech" which normally means no dirttrack oval fabricators ($2500-3500 in most areas)
There are literally a ton of threads in this section on what it cost to get to your first race and unlike Facebook, they do not disappear. You likely looking at $5-7K to get a car prepped without including entry fees or personal safety gear. If you have done a few cars, you can get that down to about $3K but never on your first car.
REALLY print out a copy or 3 of "How not to Fail Tech" and give one to anyone touching the car, keep one in the bathroom and one in the beer fridge.