2000 Kia Sportage Catalytic converter

2000 Kia Sportage 4 cyl 150000 miles

I have had an engine light on for months now, I have taken my car to the mechanic and they told me it was the Cat Con, so I got it replaced, the mechanic then told me that the Kia Sportage had 2 Cat Con and one was $100 and that is the one they replaced but the other one is $500 to replace. I have tried to look on the internet and have found several Cat Con that were much cheaper than what the mechanic suggested. I need to know the difference between the two and what each one is called.