As others have said, don't let anyone convince you you need a new cat section.
Cut the flexi out, weld a new one in, job done. I know tunnie knows the size, as he bought one for his.
As for Hellfrauds Autocentres, formally Nationwide Autocentre (and probably changed name due to the appalling reputation they had), are worse that ShitFit for making out you need to spend a fortune.
I had a backbox go on Mrs TB's Rover, so rang around. It was due an MOT in a few days, so the £37 inc P&P for Eternal was not an option. Halfords Autocentre near work were the cheapest, £46. I can live with that. So drop the car off, and walk to work, get a phone call a couple of hours later, its going to be £200+, and should they proceed. NO!
I go in, and ask them to explain. They claim there are 2 types of backbox for a Rover 25 (thats a lie - I asked to look at their screen, but they refused, stating it had cost prices on), and ours had one that was £100. And also that the middle section had failed. It hadn't. They refused to put it back on the ramp to show me.
Anyway, I nipped up to Motorserv, picked up a backbox for £37 (they matched the best price I could get one delivered for), and it was fitted that evening, and MOT'd a couple of days later.