Well said

I also own the Cheapino and made myself a keymap which is fully working. You can have a look at it here. Hooe that helps at least some bit.

Regarding the qmk toolbox: You can take the json file from one of the keymaps in tompis qmk_firmware repository and upload it in qmk toolbox. Then you can have the correct layout and you can configure it to your liking.

Honestly, not a lot of people in rented apartments can hear music that loud to "feel" the bass. If I did my neighbors would literally kill me.

Looks very cool! Especially the fish hat one is my favorite

Wow, really cool :D I'm wondering why you went with a straight line for the thumb keys instead of going for a curve (which so see with a lot of ergo keyboards). Is there any general benefit or is it just more comfortable for your hands?

One of the cheapest options might be building a cheapino. It should be around 50-70$ all in all. Though it's completely DIY and not the best option for beginners.
You'd have to order the PCBs and all the other stuff yourself and build it.
If you don't want to or cannot do that, there are already a lot of good options in the other comments.

EDIT: spelling

One of the best cheap (non-custom) options is the Alpine MusicSafe Pro (~25€).
If you wanna go for a custom hearing protection you're quickly into 3 figures. Here in Germany there are some vendors for custom stuff where you could get some "no name" custom or some brand stuff like the Alpine PartyPlug Custom for ~200€.
But with all custom stuff the price heavily depends on what exactly you want, from which brand and where you are ordering it.

In general I would recommend getting the cheap non-custom option, see if it works for you and if not you can still cash out for some custom ones. 25€ is not that big of an investment compared to the price of a custom set.

That looks kinda scuffed but really cool at the same time :D Nice job!

Small version with 2 different filters ~40€, big version with 4 different filters ~80€. All come without any kind of carry case / pouch. A bit expensive and lacking for that price tbh

Leo from beekeeb offers pre-build split keyboards like this one: https://shop.beekeeb.com/... and it's within your 350$ range.
It should check all your boxes except a dongle and rgb. Regarding the travel case: He even offers a soft travel pouch in the store.
RGB on a wireless split keyboard needs a pretty big battery to have more battery life than a day or too, so it's difficult to find both rgb and wireless in a pre built one without raising the costs. Also some LEDs draw constant power without even being on which also adds to this issue.

Idk if I'd say shocked but NTR Netsuzou Trap (the Manga) was definitely a special experience for me. Great in the beginning, soap opera stuff in the middle (I don't really like that part, so much unnecessary drama) and a nice ending.

The Cheapino gets quite some love recently :D Saw a couple posts in the last weeks, really cool! I too built a Cheapino for myself and a friend who wanted to try out these ominous "ergo mech keyboards" 😁

Thank you 😀

Ohhh I didn't even recognize there was a little switch. Really cool! Thank you

That's a really cool build, well done! I'm wondering how you're using the trackball and mouse clicks. Do you use the trackball with your index and middle finger and have left and right mouse click on the thumb keys to press them with the thumb?

Really cute ~

Looks really nice! What are those arm (?) rests?

That's a nice collection!

It's good you already answered the "Why do this?" question cause that's the first that immediately came to mind :D
Imagine going to the office, all colleagues already at their desks, you connect your keyboard and some Sailor Moon intro playing or so. Absolute dominance shown😤

I fully support the move to the fediverse. It's great seeing the community getting more active here.