MOT Fail! - Cat

[Sam3352]

argh how annoying, only had it a few months
failed on emmisions, Catalytic converter they said

and they quoted £196 + VAT for all of it inc. labour n fitting and parts
Just wondering if i can get it cheaper, fit it myself with a haynes, etc etc.?
£280 including the MOT

thanks a bunch for any help People - also, could do with a quick reply, thanks again