1995 Chevy Camaro Catalytic converter

Engine problem
1995 Chevy Camaro 6 cyl Front Wheel Drive Automatic 142 k miles

my daughters camaro is now making a loud rattling sound, it always kinda had one that u could hear slightly, but now its really loud. it sounded like the converter plate was maybe loose and needed tightening, but hence my question. apparently it has gotten worse cause when she pulled up in it, i heard it with my car door shut. should we just relplace it and what does the repairs consist of . parts? cost? any idea?
its just my daughter and i ,

and i see their faces light up when we walk in, foaming at the mouth type of look.. now normally id like that attention but not when it comes to repairs... HELP .. what do i say and how so it would appear i know what im talking about???