2007 Chevrolet Cobalt Catalytic converter

Hello, my car has been making a very loud noise ever since I bought it, almost sounds like there was a hole in muffler or something. So I finally decided to take car into mechanic and they told me the loud noise was because of the catalytic converter and that i needed a new one and it would be around 500.00. I was just wondering if it's okay to not fix it as long as I don't mind the loud noise? Will it do my car any harm by not fixing the catalytic converter or make it more expensive down the road if I choose not to fix it. I'm a student and work two jobs and don't have a lot of money, so I don't want to fix it if it's unnecessary.
Thank you :)