Here is some info on that code: http://www.obd-codes.com/p0430
A very large number of shops will see such a code and conclude that it means that a new converter is necessary without doing any further work. The only thing it really means is that the readings from your front (before the CC) and rear (after the CC) oxygen sensors are too similar. The O2 sensor voltage go up and down depending on how much oxygen is in the exhaust. The front one should go up & down a lot. The rear shouldn't. This code happens when the rear sensor readings are also going up & down a lot.
These readings can be off because the CC is bad, or because the sensor is bad, or because the sensor's wiring has a problem, or because of exhaust leaks. So before replacing a CC the other stuff has to be checked and you need a shop that will do the checking. Perhaps your shop already did the checking - we don't know. You'll want to find out.
IF you do need a new CC, AND IF you had dealt with it from the beginning it probably would have been covered by a mandated 8yr/80K mile warranty on this stuff. I think you waited too long.