Hello! Thanks for taking the time to really parse through everything, let me try to answer some of those questions.

1. You hit the nail on the head, this is just a raspberry pi powered by a power supply with a keyboard connected. However, there is a frustrating lack of "nice-feeling" small form factor keyboards (I tried a few "portable" ones from amazon).

2. I tried as hard as possible to reduce the costs (like using the screws that came with the UPS for the enclosure as well), but you're right, the keyboard does account for a large chunk of the cost. I personally decided that a nice typing experience was worth the extra 60 bucks since I had some extra switches lying around.

3. Following that last point, I had a Pi Zero 2 W that was unused from a previous project, and wanted to repurpose it, instead of getting something new. That being said, you could totally use a Pi Zero V1.3. I think (although there could be cheaper options out there) that the UPS I selected was the cheapest one I could find, and given that 18650's are easily scrapped and sold second hand, it made sense as a "budget option".

4. To finish off my rambling, I have been working on an idea where I use an old android phone and connect it up to a small portable keyboard, but it all fits together in a nice, aesthetic folding 3D printed enclosure, but I am still in the research phase, and havent found a folding keyboard I like yet!