How much does it cost to replace a catalytic converter on a thunderbird?

This mechanic said it will cost me a over a grand to replace my catalytic converter. I don't believe him. I have a 1996 Ford Thunderbird. How much would it normally cost me to replace it?|||you can buy a universal one at autozone for about 100.00 bucks.Any local muffler shop can fix it . They probably even sell them .