> For 1 burger you need like 4 pounds of vegs

In terms of calories, this is technically correct, but the metric of calories is not at all useful in a first-world context. At my local market, £1 gets you about 10,000 kcals of rice or pasta. In other words, any budget above $1 / £1 per day will be able to provide plenty of kcals. Kcals are not the problem.

What matters are the other things the body needs. I eat vegetables to provide fiber, vitamins and phytonutrients. I eat meat to provide protein and certain types of fat. In this regard, they're not fungible, because leafy green vegetables are a poor source of protein and meat is a poor source of phytonutrients.

Given energy constraints and the economics of things, meat should be more expensive everywhere. But the US also has massive agriculture subsidies, so what determines the cost of food here is Congress more than any market.

Dried beans (my favorite) tend to be much cheaper than just about any other source of protein, but I don't think I've ever seen tofu being sold for less than hamburger. Ground meat in this country tends to be really cheap, thanks to agricultural subsidies, filler, "pink slime" and the like.

I think there might be a misunderstanding about a typical vegetarian or vegan diet. Do you believe that most vegetarians and vegans eat primarily vegetables like broccoli and cabbage? Myself and others I know tend to eat a large amount of beans, grains and root vegetables as this is typically necessary to get the required daily amounts of protein and calories.

I don't think you're doing a fair comparison, which would mean comparing the cheapest meat with the cheapest non-meat foods.

Of course mince meat is cheaper per calorie than lettuce, it's probably cheaper than tomatoes, but it's not cheaper than rice or lentils.

BTW - I live in Europe too.