Couldn't you just buy Ensure or some other meal shake at the local pharmacy?
You could, but what fun would that be? :) In seriousness though, much of OP's intent was to make Soylent as affordable as possible. To that end, a quick cost comparison: You can buy 24 8-oz Ensure drinks on sale from Amazon for $42.50. Each drink contains 350 calories, so: (24 * 350) / $42.50 = 198 kcal/dollar. Rob claims to get 2629 calories a day from Soylent, and his monthly costs were $154.82, so: (30 * 2629) / $…
And no, it's not an adequate diet replacement for the average case. If you really don't like food and consider it an inconvenience, maybe—but that ain't normal. And it's not just a matter of getting used to it (goodness knows I've had enough of the stuff); normal people actually enjoy the tastes and textures of good food.