I have to mildly disagree with point 6 - it's maybe not QUITE $20, but you can assemble a few components which will make a decent Android phone into something resembling a desktop.
First you need a Miracast dongle - they're available as low as $10-$15 on eBay, though the cheaper you go, the worse the performance can be (they all use the same chipset but some skimp on the antenna...). Second, get a microUSB OTG hub so you can plug in a commodity mouse and keyboard. Third, download Google Docs or get free MS-Office.
Assembly: Plug Miracast into HDMI input of old monitor (or use $5 HDMI-DVI adapter). Plug peripherals into hub and hub into phone.
And that's about it.
I did a lot of product research on these components during the first half of this year, intending to turn it into a pocket-sized product with a custom case and everything, before dropping the project due to lack of time. So I've bought half a dozen kinds of dongle, as well as virtually every folding Bluetooth keyboard on the market (none worked well enough to be worth it for me) and about half the pocketsized Bluetooth mice, and I've done a lot of testing.
Of course this depends a certain amount on the performance of your phone (Miracast does put a load on the CPU) and the availability of monitors and keyboards. But more and more offices are offering docking stations for roving/traveling employees' laptops, which was my intended target market.
As for underprivileged students, my own kids use 4-5 year old desktop PCs my employer gives away for free and every time they get an upgrade, their old ones go to our school for the less-privileged. I just gave away a Core2Quad Dell with 4GB RAM and a 320gig HD, monitor, and color inkjet, with Windows 7 Pro. Because that's what my office was giving away LAST YEAR...