You might want to consider a Cat from your local scrappy.
I had the rattly cat problem ^^^ about a year ago on my Mk1, went at just under 200K miles...
I got a Cat from my local scrappy for £30, they said it was sound (30 day guarantee), it apparently came off a car that was driven in for breaking.
I then phoned a few Tyre&Exhaust places to see if they would fit it for me. The franchise ones wouldn't (e.g. Kwik-Fit, National etc). One of the independants did tho, for a tenner :L It took them about an hour to do, but still kept to the agreed price :L :L :L