I am fitting in an after market exhaust soon, and just wondering how often should we change the cat? and how much does it cost roughly?

 

Honda wanted...sit down...£1,300 for a new cat

There are plenty of other, much, much cheaper options. My cat was rattling, but still working after 90k miles. There are others much older than that. No need to change it until it fails, unless you want hi-flow or some other modification.

 

My local Honda garage quoted over £1k to replace my noisy/rattly cat (they described it as collapsed without evidently having looked at it properly when this wasn't even the case!).. I just stuck a £40 de-cat on instead