Literally straight-piping your car is one of the cheapest mods.
You actually have to pay more money if you want more performance and for it to be (relatively) quiet. That's one of the reasons loud vehicles are so common because and best solution for more performance is also the cheapest.
(It is more complicated than that, but this isn't the car community to where the nuances matter)
There's a mechanic advice page but not many have asked for advice. This is a shameless plug bc somehow I ended up being a part of that place and would love to see it active
None that are really worth visiting. Cars is one. I think there's a classic car one as well but there are a handful of new posts there every week which makes it mostly useless. Such a shame since Reddit's car subs (and there were quite a few of them) were quite well trafficked.
Yup. When my exhaust fell off, I replaced it with straight pipe because it was the cheapest option. I also don't rev my engine through neighborhoods, so no body cares. I can't tell much of a noise difference in or out. I think the turbocharger did most of the damping.
For a short time I worked in a factory that made school busses. They used big diesel engines and not a single one of them had a muffler. The SCR and the turbo made them plenty quiet.