Check Engine Light - Catalytic Converter

I don't profess to know a lot about cars. I have a 1996 Honda Civic LX Sedan, which I purchased new. Currently I have 102,700 miles on the car and would like to reach the 200,000 mark before purchasing a new car. My check engine light has recently be coming on and after a few days will go off. Now the engine light stays on. I took it to my local auto store and had them attach a diagnostic reader to retrieve the error code. The code came up as catalytic converter. I am hesitant to take it into a shop and have them tell me I need a new catalytic converter. For all I know it could be a falty sensor. In addition, engine idle will go up and down slightly when I am in gear and stopped. When it's idling too low the car will sputter every now and again. Can anyone provide some advice as to determining the problem without laying out a lot of $$ for a diagnostic work up by a garage?

so go out and buy a new cat put it on see if the problem continues

yeah cat converters arnt very expensive
just go buy a new one and see if that fixes the problem

muffler shops sells catalytic converter at a reasonable price and installation right around 130-150. The problem is that your cat might be connected to your exhaust manifold which cost much more money. You might want to see what type of cat you have and see what shop can give you the best price.