The propagandists for the 'plant based diet' have been bothering my subconscious lately, until it finally percolated up into my consciousness. Cows ranging across a field, eating grass consolidate PLANTS into to highly nutritious beef. If you buy good butter, you can actually taste flavor variations that depend on what grasses were eaten and when. Spring butter tastes different from fall butter.
The problem with a 'plant based diet' is that all diets are 'plant based diets.' This sort of nonsense leads people to make critical errors. If you are on a budget, stop buying lettuce, and buy meat instead. Lettuce is a luxury good. It is superfluous to your diet because anything that may be contained in is easily and more cheaply obtained elsewhere.
The real problem lies, not a plant versus animal argument, but in what humans used to eat, versus what the U.S. government has heavily subsidized since the post-WWII era. Soybean, corn, wheat, canola, etc... You can avoid a multitude of evils just by avoiding wheat, soy, casein, and vegetable oils that come from crops grown in fields.
What did humans used to eat? Meat (including organs- 4 ounces of liver equals about 5lbs of fruit), eggs (especially the yolks), seafood. They would cook in natural (i.e. not hydrogenated) lard, or butter from grass fed cows. Olive oil, coconut oil, and palm oil are pretty good too. These foods take care of the bulk of your nutrition and calories.
Tubers, preferably the ones with beta-carotenes and other bright coloring agents, which tend to be antioxidants, are the next on the list.
Fruits and vegetables are third. Vitamin C. More bright colors.
Then there is the green stuff, and the best green stuff is not kale, but the stuff we now normally think of as spices or garnishes. Parsley, cilantro, rosemary, basil, etc...
Of all the grains, white rice doesn't seem to be too bad, assuming you can handle starch. I would assume these are 'empty calories' and pair rice with very nutrient dense foods and spices.
At the end of the list is lettuce. This is what you eat if you are rich and you need a novel salt and fat delivery device. If I remember correctly, even the word salad derives from the Latin name for salt. And, yes, even salt is more important than lettuce. Especially if you sweat. This is really important to remember if you get away from processed foods and try to eat healthy, because you need to be sprinkling salt on your food to taste or else you will find yourself going quite wobbly.