My brother-in-law's car has just failed inspection. One of the items listed was a "cat-back." Since the bill is astronomical, I was wondering how much of the exhaust system is encompassed in this term and what is the relative ease to change this on a 97 Pontiac sedan?
The cat back is just that the exhaust pipe including the muffler from the catalytic converter to the end of the tail pipe. Seems odd to me, not impossible just odd that you would need to replace the entire exhaust system from the cat back to pass inspection. I see from your profile that you are from PA and road salt can deteriorate an exhaust in that time-frame so it actually may be that bad.
It's not difficult to change unless it's rusted really bad, if that's the case you will want a lift and a torch.
Based on the "astronomical bill" I would get a second opinion.
Go around to some local shops and put their estimates against each other (openly) to drive the price down. There are a lot of "universal" pieces that can be used in exhaust repairs. I had everything (converter to the tail) replaced in my old Corsica (10 years ago maybe) for around $100. Of course this was no high end exhaust, but it was a Corsica. ;) Lasted until I sold the car some 6 years later.
I can't see it being astronomical - that is one of the expected regular replacements here in the UK (where we do get a lot of corrosion due to salt) but it is a quick half hour replacement and it is pretty cheap kit.
I don't know the Pontiac so I don't know whether there is some custom piping in there, but that seems odd.