Oxygen sensors are one of the least reliable parts on a car. Why? They're hanging right in the hot exhaust stream, not the friendliest of environments. That hasn't stopped car manufacturers from liberally applying multiple O2 sensors all over the exhaust system (before and after cats on both (dual) exhausts), etc. Most performance cars have at least four O2 sensors, which makes your odds of a failure in the first 6 years or so fairly high. Add to that the fact that the wiring to the sensors is also at a high risk of being damaged.
Keep in mind the failure may only occur while driving and while the ECU runs a particular diagnostic test. It takes a variety of driving (steady state cruise, cold start, etc.) to get all the test run flags set in the car's ECU, which is why a smog test will fail if you clear all the codes and immediately go get it smogged. You need about 30 miles with some highway miles included to get all the diagnostic tests to run, although it can happen sooner if you know the conditions that will initiate a diagnostic test (these run undetected by the driver).
Four-wire heated sensors for my Gen III run $38-110 each in the aftermarket, more from the Dodge dealer. Plus figure about 30 minutes labor to install it.