I really liked my Keebio FoldKB, which I wrote about here, although for me the main attraction was its similarity to a standard keyboard, which sounds like it isn't a consideration for you. I currently have a Moonlander, and the last time I was going on a trip, I packed it up but said "f*ck it" because it was just too cumbersome, and just relied on my laptop's keyboard. I've taken my FoldKB on trips before, though, and it was much easier to take along. I think I will continue to use it on trips.

Ergodox EZ is fantastic, I've got zealpc zilents installed in mine for silent tactile. Expensive switches, but I've been transplanting them between new keyboards. I got the EZ from a friend when he wanted to go to a moonlander.

For a silent and portable keywell you’ve basically only got the Glove80. Their new Cherry Blossom silent switches is where I would go. Voyager is also an option but only slightly less expensive than the glove and you lose the keywell. I’d definitely go for that if you’re willing to drop the cash. There’s usually a few used ones up for sale on the MoErgo discord

Glove80 is probably the best commercial option, but is very expensive. For the combination you are looking for, DIY might be a good solution, depending on how adventurous you want to go. Linear choc/low-profile switches are not loud, but hard to silence. If you want silent, you'll need to tape mod and lube them (search up how). That isn't difficult, but is time-consuming. If your time is too valuable, there are sites available where you can pay people to do it before sending keys to you.

I recently designed a super easy-build portable board that I put together in an hour, for $80 and only very basic soldering skills. Shipping takes a while though. The low cost comes from having few switches/keys and using a chinese microcontroller. If you aren't ready for that few keys, there are options like the kyria or Lily that are bigger.

For portability, I'm just in the final stages of completing this 3D printed case generator that holds the two halves of a split keyboard together magnetically, protects the PCB, and has quick-unfold tent legs that you can customise at design time for your desired tenting. You could use this for whatever custom PCB you chose.

I think kinesis nicked the design?

Idk which is older but didn't they both blatantly copy the Ergodox layout?

I have commuted with an Ergodox and I honestly just find it a bit too large. If you are set on that many keys I'd suggest you check out SliceMK since they made a low profile Ergodox. I'm not a fan of ZSA since they are overpriced (cheap plastic) and haven't really ever done anything innovative IMO. Although I don't use it often my SliceMK wireless Ergodox is really solid.

I specifically selected the Moonlander because I travel often and needed the small form factor, while also retaining the split design and large number of keys.

The Keyboardio Atreus is very inexpensive and portable, relative to your other considerations. I have used this board for 3 years and it gets my personal recommendation.

I recommend a Cornish Zen if they ever get a restock.

I use this as my office keyboard and it's been great.

way smaller, but a good compact package as an ortho, is the reviung41. here is the kit. I couldn't get used to it though, I prefer more keys.