I have no clue what cats go for..........enough that people swipe 'em though! I saw something on TV not too long ago that people steal them and turn them in to recyclers -they get some pretty decent $$ for 'em. They are filled with platinum, palladium and rhodium.
big fines if you get caught taking them off. big fines for the inspection station that puts a sticker on it too. cats now days flow almost as good as open pipes so there isn't really much HP gain without them. not like the cats from 15 years ago.