2004 jetta needs help

I have limited info on this car(belongs to my brother-in-law)..
2004 jetta gl 2.0, 200k+ miles.
He had it to the local vw dealer.
It needs a new cat converter, a new muffler, has a rusted undercarriage and (this is new to me) a black film entering the cabin from emmissions, price quote was 2000+ for everything.. Is this a good deal? How hard is it to replace the cat and muffler?
But my main concern is the rusted undercarriage and the black film coming in the cabin! Any thoughts , suggestions are always appreciated.. Thank you for your time

First of all, if you take it to a dealer, I believe the repairs are going to cost you 50% to 100% over what they might cost at any ordinary auto repair shop - an independent one, not part of a franchise chain.
A new cat converter and muffler are not that hard to do, typically, and I cant imagine its any worse on a Jetta. I would think it would cost you $500 to $600 at a non-dealer, non-midas place. As for the black film entering the interior from emissions -- that is mysterious. Either you heard something wrong, or they didnt explain it right. Does that mean that some black smoke is getting into the interior and leaving a black coating on things?
If there was nothing else wrong with the engine, I wouldnt think it would need a new cat. converter yet, unless the problem was a rusted converter.
Rust on the undercarriage after 200k miles wouldnt be a big surprise; but it would depend where it lived. If its in a state using salt on the roads in the winters, then it probably needs to either be scraped clean and painted with something like rustoleum, or just rubbed all over with a coating of axle grease.