Question about vegetables intake

Hello Reddit, I was wondering about something like a showerthought, but that seems too important to not ask experts :) Since it is healthy to eat a considerable amount of vegetables in your diet, but since it is also expensive, especially nowadays ; Which vegetables are the healthiest? By that I mean the most cost-effective health-wise. Some cultures don't grow massively diverse amounts of vegetables like in West Africa, where you find different types of leaves, cabbage, okro and that's mostly about it. I feel like most people eat most of the time onions and tomatoes as base ingredients for stews and stuff, is that enough?