Catalytic converters are expensive due to the precious and valuable metals used to make the catalytic converters.
Catalytic converters are made with 3 types of those precious and Valuable metals that make the catalytic converter work.
Those precious and valuable metals are rhodium, palladium and Platinum but when the stock market begins to get unstable investors buy into more of those metals which drives the cost of those precious metals up even more which makes the Catalytic converter more expensive.