I dumpster dive! I don't know how feasible this is in other nations, but here in the US there's plenty of good vegetables and fruits for the taking if you're willing to dig for them. Without going into great detail, I'll say I'm able to follow a 'paleo'-type diet of only meat, fruits, and vegetables (LOTS of vegetables) without spending a dime. It's still far from optimal, as most of the vegetables aren't organic and the meat is factory-farmed, but assuming one could plot some sort of cost-health continuum I'm fairly certain my methods would rank pretty high. I do spend some money on supplements though, namely fish oil and magnesium.
>I have always thought it is absurd that people should have to buy expensive fruits and vegetables to stay healthy, when modern food processing means we can obtain necessary micronutrients for fractions of cents.
Like >>23974 pointed out, nutrition is a bit more nuanced than just getting the necessary micronutrients. Although I can't list specifics, I know there are many different phytochemicals present in fruits, vegetables, and herbs that exhibit different antioxidant and anti-inflammatory effects that are important to health. And I suppose things like cup ramen could eventually be engineered to contain all of these compounds in an optimal balance, but is it really that much cheaper? I admit that I haven't bought anything like instant noodles in ages, but calorie-for-calorie are they really any cheaper than things like potatoes or even white rice, which is going to be quite a bit better for you than instant noodles? I guess I just never got ramen/cup noodles' seeming ubiquity in the otaku/neet world.