Actually, the reason these things are worth so much money is that they are ROBUST. Land Rover threw big cats at these gas guzzlers to keep emissions down. 200k miles on a Y-pipe with original cats is nothing. Not trying to rub it in, just trying to set the record straight. Nothing wrong with a DEC replacement from Amazon, just don't expect it to last 20 years. There's also nothing wrong with straight piping it if you can stand the noise and droning. While it's not helping the planet, every day thousands of "poor emitters" are coming off the road so one Disco spewing unburnt hydrocarbons isn't going to move the needle much. You may find that you need those O2 cheaters in the rear position though if a continual CEL bothers you.

 

So how much, then, would it cost me to replace Cats, pipes, and mufflers?? Anyone do an exhaust replacement? Easy or difficult?

 

If you just want to do the front Y pipe with the cats then it looks like $388 shipped for the pipe. A couple of gaskets if you're feeling punchy, This is a super easy job as compared to most repairs. The front cross brace can give you a headache if those bolts are rusted in place. Get them off by whatever means necessary, if they break/strip you may have to drill them out but that's not too horrible. The only really watch out is the 6 manifold outlet nuts. The studs like to snap off so spray them liberally before attempting. If that happens then it's a PITA job to remove the manifolds and drill those out, but you can use bolts if the studs break. Use a 6pt deep socket with appropriate extensions/swivels on those and take your time. You may want to try it with a 1/4" drive setup and see if that will break them free. It's easy to overdo it and snap them so if they put up a fight, give up and try more spray. The two nuts at the outlet aren't usually a problem. Confusingly, there is no gasket there. The rest of the exhaust is made from 400 series stainless and will usually outlast the rest of the truck, definitely outlast the frame... Haha

Here's a link to the y pipe.

 

I took the Y-pipe off and on without lifting the truck, you can do that on your driveway. The hardest part is getting the rusted nuts off.