1999 Toyota Camry bad smell at 65 mph +

1999 Toyota Camry Mileage 80,000. When I drive at speeds 67+ mph, there is a really bad smell that comes from my car. My ex, who is a mechanic, said it was the catalytic converter, but said it wasn't a problem, and that it's expensive to replace etc. I like to drive fast, so I always smell that odor (like rotten eggs and burnt rubber), so I was wondering what I could do to fix this? If I have to replace the converter, how much should it cost? Or if there is something else that could be contributing to this smell that my ex over looked? Any insight would be appreciated.