How familiar are you with torrents? I can send you an invite to a private tracker full of 4k remux documentaries… I just think you are better with 1080p if watching on a laptop. For me at least, I can’t tell the difference (and I have a 4k screen on my laptop)

And there are cheap options on aliexpress that are solar powered

Go for the second hand 1l pcs. They are better and cheaper (but less sexy) than the zimaboard. The ones with a i3-7100T should handle like 10 transcode, if 1080p. Chrapes I’ve seen on ebay was a prodesk 50bucks. But it’s a rare deal