Total meal replacement shakes exist, although I have no idea about pricing. However, going down this route is basically ensuring sub-optimal nutrition. We know a ton about nutrition, but not enough to have an optimal diet without food.
I looked at what's available in Finnish pharmacies, and they seem to be in the $20 a day ballpark mentioned elsewhere in the thread if you aren't going to eat anything else.
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.