Exhaust

It would be worth getting a quote from a local stainless steel exhaust fabricator to compare with the MB replacement price especially if you plan to keep your G for some time.

Don't rush into deleting silencer boxes. I had a stainless system made for my GEL300 and thought it would be a good idea to modify the system so it didn't have to cross over the rear. I reduced it to feeding into one long silencer on the drivers side and then exiting on the same side instead of feeding into another two silencers and exiting on the passenger side (RHD Vehicle).

The result was a lovely deep growl which was very satisfying when sitting stationary blipping the throttle. Definetly not so satisfying when cruising along at anything over 40mph with a constant roar of exhaust behind your right ear. I can say from experience that MB knew what they were doing when they designed the exhaust system.

Here is a schematic of a 2002 G500 exhaust system in case you dont have one.
 

The essence in the question is why are the exhaust in need of replacement, if there are blows which are beyond economical patch repairs that's fair comment, if however the comment was made cause the outter skin is shabby looking then you have more life from the system then made out to be. I have noted that the outter skin and mounting brackets fair worse than the inner skin so as long as you have no leaks then you should be O.K., but take note this as to mean that you are now saving a budget for the job. 

Idea of comparing costs of the whole system, part system from M/Benz and a Stainless Steel version is worthy exercise. 

Also a system that has last you some 19 years is not bad going.

Freddie.

Before doing anything else, make doubly sure that it really is the exhaust that's the problem.

Does it rattle when the car is standing still or only when you're moving along?

A while ago I was convinced that my exhaust (that's on a G300 SWB not a G500 but even so). The garage put it up on the lft and checked all the supports, brackets etc. but couldn't locate the exact problem. Then they checked the rear shock absorbers and springs and "assumed" that one of the shocks had gone.

I almost pushed the BUY button on purchasing a set of shocks and springs but then had a lightbulb moment. I wedged a bit of towel in the rear door, drove the car along potholed road and - NO rattle.

I replaced the plastic door supports (MB price £45) and cleaned and greased the locating hole above the top hinge and all is now well. Close to £1,000 saved.

If it is the silencer boxes, think long and hard about replacing with "nice throaty sporty" boxes. They might sound great to start with but they can become really annoying/draining after a few hundred miles on the motorway.