Accelleration Problem, Catalytic Converter?

Hello, I have a 2002 Chevy Malibu, v6 3.0 engine. 83,300 miles.

My car has severe difficulty accelleratiing, taking up to a minute to hit 40mph, and rarely can ever get above 50mph, with the "pedal to the metal". I had a diagnostic done at a shop and they said my catalatyc converter is the problem. They said it might need repairing or replacing, but would not do anything except charge me $600 to replace it with a new one. I took it to Chevy and they said it'd be close to $1,000. My question is is there any way to get it repaired or fixed cheaper? I really don't want to pay $600 for a piece if I can avoid it!

And to make me more irritated, I find the federal emmission warranty is 80,000 miles. 3,000 miles less than what I have! ARRGH!

Thanks for the help!