yes it is serious a clogged converter can cause fire. If the car is not performing as it should the excess emissions build up in the converter. These converters get very hot, which can lead too dangerous and often fatal fires. Repair costs differ, you can buy one at most major parts stores like autozone, napa but the biggest cost savings, is being able too install it. It is no walk in the park I have done few of these it is not fun. That is where it get expensive. Plus if you live in a state that tests for emissions, your car will not pass with a defective converter.
thankyou!