I don't know about "all the knowledge ever", but to give you a baseline, the entire Wikipedia with images but without editing history, as last archived by Kiwix in May, 2022, is 90 Gb.

A web server can run just fine on e.g. Raspberry Pi Zero W ($10), exposing any such content to any smartphone etc able to connect to it via WiFi (Kiwix sells preconfigured SD cards for their content, even). So, assuming that most people already have a phone or a laptop or even something like a Kindle, the only non-negligible cost here is storage. And a 1 Tb SD card can be had for under $150 right now.

So if anything, I think OP is overly conservative, given that their estimate was "$200 per person". Unless that counts the devices used to consume the content, and not just storage and the server.