2001 Toyota Corolla Catalytic Converter problem

Hi,
My car check engine light is on and the service center scanned and suggested to replace the catalytic converter and estimated a price of 1400$.
I found catalytic converters online for < 300$, is it worth at spending that much (1400$) at authorized service center instead of buying parts online and fix it with a local machanic?
I want to sell this car next year any way and so I dont want to spend much on its repairs. By the way, how long does a car with a bad catalytic converter run?

Please suggest me. Thanks in advance.