Q: What should I try fixing first?

5 days after taking my car home, the check engine light and 3 others came on. The dealership I bought it from wanted to charge me $3,000 out of pocket to fix it and told me there was nothing they could do. A few places have read the codes and I even read them. They all say the same thing: P0430 bad catalytic converter. One man even listened to my car afterwards and said he thought I could have an exhaust leak. I'd rather just take the cat converter off completely than pay $3,000 to fix it. The other 3 lights were the slippery when wet, vsc trac, and vsc off. They all came on at the same time. I've heard when the CEL comes on, they automatically do too. It wasn't raining when they came on. My cars not loud. It vibrates a little, usually when given gas. When I give it gas, it doesn't feel like its going as fast as it should. I get around 15 mpg. It seemed very well kept by the previous owner. So what all could make the CEL glow for a bad cat converter. What should I try looking at first?

My car has 160000 miles.
My car has an automatic transmission.