My Nissan needs a catalytic converter?

I also own a 2000 Nissan Maxima V6 with over 100,000 miles. I just had one of it's catalytic converters replaced back in May. A good mechanic with the proper emissions equipment can tell you which converter needs to be replaced when they run it on the computer. Unfortunately, it's not a repair job that can be done at home and eventually the other converters will have to be replaced as well. It's sort of like a chain reaction with each one. I am about to replace a second converter on my Nissan. Make sure you find a good mechanic who knows what they're doing. I don't believe the part has to be directly from Nissan. I think my converter was ordered from a manufacturer who made parts for Nissans. It probably saved me money not going directly through Nissan, but overall, the entire job cost me about $900.00. It looks like the front cats are built into the exhaust system. Check out the images (Below). Please let us know what happens.

I don't drive my car in the winter so it has pretty low mileage, 89k, and since winter is almost here, I have several months to save the $ to do it. I really love this car so it's worth it. I am just trying to find the least expensive way to do it. Your information was very helpful. I was thinking this would probably be the case. Thanks for your input!