Trying for a rough estimate of the yearly cost of taking a multivitamin daily, I get about $10 USD a year. For the 15% of the global population that live on less than $2 a day, that's around a week's wages. For the 56% that live on $2 - $10 a day, it's slightly more affordable, but still a significant cost.

Now, that's a cheap multivitamin, so it's got about 300IU of vitamin D, which is a pretty small dose. At a guess it's probably cheaping out on some of the other ingredients as well. On the other hand, ingredients bought in bulk and distributed through outlets in the developing world with very low overhead might be more affordable.

EDIT: the numbers for global poverty are probably out of date, but you get the point