hi, as 2006 Pathfinder owner, I do really feel your pain 
are you really SURE you need it?
replacing downstream and upstream sensors is more likely to be needed than replacing cat itself
what is mileage?
what is oil consumption per 1000 miles?
If you REALLY want it, I used Shultz first and quality was subpar, so I went Pacesetter and it worked great:
what is the OBD code?