just bought a used '02 civic...po420 code
 

Just bought a used '02 civic, had it inspected by a mechanic (I know nothing about engines), he said it was in great condition. It feels nice except shakes a bit when sitting at red lights. I don't hear any weird sounds or smell anything odd.

2 days later, the engine light comes on and it's code po420. A/F ratio concern, air leak near ho2s (heated oxygen sensor) bank 1, ignition system concern, or faulty catalytic converter is what the paper says.

I don't like gender stereotyping, but I am female, and so mechanics love to try to rip me off. I am living in a new area and don't have anyone I trust, and my boyfriend doesn't know engines. Just wondering if anyone has experience in this and knows how much I should expect to have to pay to get it taken care of?

Also, will continuing to drive it for a few weeks do any permanent damage?