Auto body repair & detailing: Catalytic converter, isuzu rodeo, lung tumor

Question
Last week, my check engine light went on, so I immediately took my Isuzu Rodeo to the dealer repair.  Their diagnosis: the catalytic converter needs to be replaced.  The cost?  At least 3 thousand dollars plus, if one considers the amount of work hours involved, which from the way they tell it, would be considerable.  

The mechanics did say that the car was still drive-able, and if I were to decide not to go through with the converter replacement, I should be able to get around.  Oh, and incidentally, they mentioned that all the other auto parts were in perfect shape--which feels like telling me that I'm in great health, except for that annoying lung tumor.  

What do you think I should do?  I've already turned down the replacement and decided to take my chances with the vehicle until it breaks down; I just feel like it would be cheaper just to wait and buy a used vehicle.  (The Rodeo in question is only barely 5 years old)  Better that than to put more money into a vehicle that just keeps eating my money.  Also how critical is a "catalytic converter" to the overall health of my car anyway?  Is this something that can lead to complete disaster years down the road--or tomorrow?  I appreciate your help.

Answer
Hi Repair rookie ,
I also am a rookie when it comes to the drive train of the cars,I am a Autobody Mechanic who specializes in the body repair and refinishing...I will however say that that seems to be a huge amount of labour and part cost??? I would get a couple of other opnions from some of the shops in your area....Also check out catalytic coverters on line... Hope this helps you out.....Kim