[OutOfHere]

I don't know of any singular resource, but if you ask me here or in r[eddit]/FoodNerds about a specific vitamin or mineral, I will be happy to share what I know. You can message the mods there if you want with a specific question.

The FDA doesn't set the values, and be glad they don't because they're very corrupt in ways you wouldn't realize. If it were up to the FDA, every product that doesn't pay the FDA a bribe of $1 million for "certification" would be banned, and then everything would cost the consumer 10x. You would also then have to pay a useless licensed practitioner for the privilege of buying anything, typically at a dose that would be too low to improve health. The NIH ODS sets them, and you can read them at https://ods.od.nih.gov/factsheets/

There is no standard because each vitamin and mineral is unique and special. There are some heuristics, but they only go so far. For example, an ideal dose is often (but not always) close to the average of the minimum and maximum limits.

And believe me when I say that I do my best to keep the cost as low as possible while keeping the quality good enough.