Lentils are pretty much nature's perfect food when considering cost, protein and fiber content. Additionally, lentils are low in methionine. I don't put much stock in methionine restriction for human longevity, it does work in rodents, so if you want to be a guinea pig (couldn't resist) they're good in that respect too.
Eggs are also excellent for their high essential fatty acid content, and this may sound counter-intuitive but if you eat a lot of beans dietary cholesterol is actually beneficial. High quality eggs are also a really good source of vitamins E and D.
Finally, though they're unfortunately not so cheap, hemp seeds provide you with both omega-3 and omega-6 fatty acids and minerals. A mix of sunflower or pumpkin seeds and chia seeds works well and is cheaper if you're optimizing for cost.
The only vitamin that I think is worth supplementing is niacin. Niacin has been shown to increase BDNF levels in animals which can help with mood and memory formation, and it has also been shown to increase lifespan by 10-15%. For people who don't go outside and don't consume much milk vitamin D might also be a good idea.
Interesting, I have found some references to beans lowering cholesterol but not this stronger statement?
I've read that the link from dietary cholesterol to body cholesterol levels is genetically variable, but that there's no test at present for determining individual risk factors.
Based on these parameters I can judge any food based on whether its fiber and protein can match (or beat) a linear combination of chicken and broccoli. Basically if (2F + P) * 20/3 <= C then it's on the diet. This includes non-fat yogurt, wheat bran, eggplant, and some types of beans.