mad,
I don't know of anyway to "defeat" it , just "comply" with it. And yes , price varies greatly depending on the muffler type you buy( from $100's to $1000's)
It can be defeated with switchable exhaust. That can be changed from thru hub to thru hull , but those are also illegal in NH.
I had one exhaust system inspected by the MP for that same reason. When I come off plane the exhaust quieted down like I switched it. It was just that the exhaust wound up under water at an idle and headway speed.
