2001 Jetta (1.8T) - check enginer light & vibration

I drive a 2001 Jetta (1.8T; 97,000 Miles) and got my oil changed at a local Jiffy Lube yesterday.

This evening, the check engine light started flashing and the manual says that this could be problem with the catalytic converter. I see additional symptoms:

1) Power has come down
2) There is lot of vibration inside the car, especially when stopped at a traffic light (even my 7-yr daughter felt the vibration)

Is this a problem with the catalytic converter? Or could it be something else? Approximately, how many $$ would I have to spend?

Any pointers would be helpful

Thanks,
Karthik