What is a reasonable cost to replace the catalytic converter?

This site will give you a good idea what it will cost based on where you live , see below copy and paste

http://repairpal.com/

Have a mechanic check it- don't just guess- if you smell gas inside the car, that is a dangerous condition- there may even be a couple of problems at the same time- having said that, a cat is expensive- they have precious metals inside which work chemically with CO- that is why thieves like to get under SUVs in the middle of the night and steal them-

Don't put it off either, just read in the news an 8-yr old died from fumes from a missing catalytic converter while driving around a couple hours with his father.