Someone I know just seriously damaged their 2005 VW Beetle and it may not be worth fixing (drove over a divider and at least broke the transmission). The car has approximately 34k miles on it, if I remember correctly. My mechanic recently told me that the catalytic converter in my 2.0 L 2004 VW Jetta is starting to get clogged, judging by the 80'C temperature drop between input and output and that he thinks the performance is not good enough for a 2L engine. The Jetta has about 92k miles on it. Is the cat converter from the Beetle compatible with my car? If it is, would it be worth the effort of trying so salvage it from the Beetle, assuming it isn't damaged, and what would be a fair price to offer?
Looking it up on RockAuto.com, it shows for the 2.0l SOHC engine (they do not list an option for a 2.0L DOHC in the Beetle), the catalytic convertor which is offered there is a direct fit for 2001-2005 Beetle and for the 2002-2006 Jetta (as well as the 2001-2005 Golf and some even have it for a Mercedes model ... argh). This would seem to me to mean the cat in the Beetle should fit over to your Jetta without the need for modification. I think there is a flex pipe at the head (where the cat pipe connects to the turbo), so any small variance should not be an issue.
As far as cost of a new one, examples from rockauto are in the $250 range. Just throwing that out there.
If the Beetle is the 2l version, then they have the same engine, so you should be good to go. I don't know however if the section of pipe that the cat is in is compatible with the Jetta. These things are pretty cheap, relatively speaking. I would be surprised if they cost more than $100 to $150 (I don't know where in the world you are, but everyone knows how much a dollar is worth in their local currency).