You can either get a complete new section of pipe(I suspect this is expensive),or you can buy a new section of flexi-pipe and have it welded into the original pipe.The flexi pipe is available in various diameters,and if you know someone who can weld to a good standard,this is the way to go to save a few quid.
the same part has gone on my laguna. took it to kwik fit and they said the have to replace the part, which includes the cat and quoted £213.
i e-mailed renault and they quoted me £437 just for the part. looked aroend a few websites and found that one called gsf car parts have the part for £84 +vat. im gonna get local garage to fit it but if you can do it yourself then even better.
hope this helps.