I ordered a custom set a good time ago (months before the existence of this community) and the experience was comparable to yours.
I choose white mbk pbt and the laser engraving was really sharp and looks very good! Shipping was quite fast for me (8 days or something to Germany) but back then VAT was no accounted for during ordering (which I was informed of, no suprises there). So I had to pay VAT after receiving the package. Don’t know how it’s currently being handled though. Simon was also really responsive, so all in all a quite good customer experience.

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” 😁

Nice case! Basic but functional, pretty good for a first

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?

That’s a really interesting case design too! Cool to see that you’re taking into account that one might bring it into the office or so and needs a “travel” case as well.

That’s a really cool and funny solution :D

Galaxy Watch 4. I don’t like Samsung but I wanted WearOS 3 so yeah…

Cool! I’m happy it actually helped you :)

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.

Cool design!

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

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?

Regarding documentation, you could have a look at splitKBs Aurora series build guide. They made their own Sweep variant but it might just be similar enough to still use it as a nice build guide for your ferris sweep.
EDIT: It also has a part about installing batteries, power switches and all the other stuff needed for a wireless build.

The first time a mouse interested me more than the keyboard :D Cool setup!

I already have a set from FK Custom. The laser engraving is very good, clean lines, nothing blurred or rippled or so. It’s definitely high quality.

Leo from beekeeb offers pre-build split keyboards like this one: https://shop.beekeeb.com/product/pre-soldered-wireless-dao-choc-ble-keyboard/ 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.

That’s a nice collection!

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

That’s a good name 😂