How much does it cost to change a catalytic converter?

I went to a mechanic %26amp; he told me that there was something wrong with my 2000 Toyota Celica's catalytic converter. I am going to a different place tomorrow but i wanted to know before hand how much i would have to pay to get it fixed.How much does it cost to change a catalytic converter?buy new one from auto store and have a muffler shop cut the old one/ones out and weld yours in. 50-100$