First, Andrew, that Grizzly is only $50 because I'm assuming it's only 6". The model/manual I opened up was 65, 66, 67, 68, etc. I assume that means six inches long by 5/6/7/8 inches diameter. Think about a sound wave or wave forms, you are going to need internal baffles and redirection to kill them --so length is key. 6" long will be better than nothing, not not nearly a silver bullet.
Martin, do you know what oakum is? (it's like manilla/hemp rope fibers, untwisted) My current home was built in 1954/5. Back then they used cast iron pipes then they packed the joints with oakum and poured hot/liquid lead into it to seal the joints. When I redid our main bath the DWV (drain waste vent (the poop vent)) was cast iron with oakum joints. To be honest replacing that with PVC was probably the easiest and cheapest thing I did in our house.
The only problem was that the PVC was loud and you could hear everything through the new 1/2" crappy drywall/blue board/cement board.
When I was a punk kid I was into boom-boom car stereo systems. We would tear up our carpets and line our floors with dynamat, roofing tar paper, etc. Mass or density kills sound. You could buy a bag of Roxul Safe & sound or equivalent bag of the Pink Panther brand (owens corning) mineral/rock wool insulation. Break it out into strips then use black (tar) flashing tape to wrap your pipes. In our bathroom simply wrapping the 4" PVC DWV with two layers of flashing tape made a HUGE difference. It's about the density to absorb the sound.
If you have drywall you could always look into Green Glue. I did my home garage with Green Glue between two layers of 5/8 on the walls and two layers of 1/2 on the ceiling. It's so quiet now that I worry if I ever got hurt I'd probably yell and no one would hear me...
If you vent outside, a short resonator pre-filter combined with a longer resonator post-filter would make a huge difference.
Lots of race tracks have sound/db maximums. Many tech inspections measure sound. There's lots of info about this topic on car forums all over the place. The Aussies tend to be pretty crafty and come up with a bunch of innovative stuff for their V8's.