At the end he write the setup cost him $20, but the display alone sells for $50 (from the amazon link he provided). I'm assuming he had a bunch of the components already, but that's not really a fair cost comparison.
But I'm assuming in that setup you have a VGA-capable monitor on a shelf somewhere; not everyone does, of course.
In the video I mention the all-in cost, accounting for the monitor, keyboard, mouse, power adapters, etc.
This isn't a practical setup by any means, but at least you wind up with a neat couple bits of hardware that could be repurposed once you get bored of it!