Cabbage + brain damage

Eggs with salt. Boiled, scrambled, any style really

Lentils.

Well, something being delicious is subjective, but if we assume a "general acceptance" of most delicious foods, potatoes could fit easily. They can be cooked in all kinds of ways, are very nutritious and, again, pretty much everyone says they're delicious.

I don‘t know about economics, but this is my entry to research:

https://youtube.com/watch?v=0Xa7Dp3-eYA

And cucumber prices went up more than 50% for me in the last 2 years alone, so maybe you‘re onto something.

How is rice healthy? It's just something to keep me full.

Pizza is pretty cheap in Italy, also Pasta.

I'd say sandwiches, depending on what you want to put in them. A loaf of healthy (low sugar) bread isn't going to be the cheapest option on the shelf, but if you're dividing the cost by the number of sandwiches you can make out of it, it still ends up amounting to a large number of really inexpensive meals. I normally just add some meat, cheese, lettuce, and tomato, and it's very nutritional and also delicious.

The one thing missing from the trinity is "effort". For instance, you could make any Dal, which would fit the trinity, but takes a lot of time. There are books with hundreds of Dal recipes that all taste different and work, too. And this is just one example. Less than a dollar a meal if made in bulk with rice.

BEANS

Addictive carbs and salt, dirt cheap, and healthy as shit. Also convenient and compatible with most dietary/ethical restrictions.

If you learn to like beans when you're 20 and throw it into an index fund, you'll have a modest retirement fund just on the money you saved (yes, I calculated it based on money saved and growth of the S&P).

And then there is mc Donald's and similar chains. They managed to avoid all three of those things