Yudkowsky's 2014 April Fools Day's confession notes that food production could be more efficient:
Food in dath ilan was made by people who were very good at making a particular variety of food, and they’d pick a few dishes and make a huge amount of it on any given day. There’d be many places like that within 2 miles of you, and a small courier-carlike-thing would attach itself to another car and arrive with the food you liked within 2 minutes.
A quick Google search suggests that restaurants tend to spend around a third of their revenue on ingredients (more quick estimates of restaurant operational costs on page five of this slideshow). Of course, fast food and fast casual restaurants spend a higher percentage of revenue on ingredients than other types of restaurants, but spending 30-35% of revenue on ingredients seems standard. So, it should be possible to reduce the cost of food by producing food more efficiently, that is, by making huge batches of one or two types of food at a given restaurant.
I've only been able to find one example of an establishment that actually does this. Ugi's, an Argentinian pizza chain, sells 12-inch (?) cheese pizzas for about 4.91 USD in Buenos Aires. Ugi's has a couple of locations in the US, too-- this one in Boston sells 12-inch cheese pizzas for 6.55, but also sells items other than cheese pizzas. For comparison, a 12-inch cheese pizza from Domino's pizza costs around 11 USD to order via carryout in Boston.
I, for one, am fascinated by the idea of restaurants that only serve one item, and would definitely purchase food from such establishments if they were more common in the US.