This seems like something you could make yourself for under $50. Pi Zero W2, battery, cheap LCD screen, and 3D-printed case. The only exceptions would be a) the extra physical buttons (requiring a custom PCB) and the amber backlight (not sure if you can get a screen that comes with one, or if you’d need to get it separately and install it yourself).
If I had more experience in making stuff like this (and money to buy the components and other tools I’ll need to make it), as soon as I saw the price of this thing I would have started making my own clone right away and thrown the code and hardware specs on GitHub.
If I had more experience in making stuff like this (and money to buy the components and other tools I’ll need to make it), as soon as I saw the price of this thing I would have started making my own clone right away and thrown the code and hardware specs on GitHub.