I think it would be fair to charge users in higher-income countries (a bit) more so users in lower-income countries can pay less. The question is if this could even be implemented. I'd guess that, if the fees for Brazil were lowered, there'd suddenly be a LOT of Brazilians using Kagi.
If there's hesitation to raise the fees for higher-income countries (which I'd understand) this could be done on a voluntary basis, but the question remains how to even identify those who deserve a lower fee.
Maybe this could be solved by taking into account the search region: I doubt someone from the US would set their search region to Brazil just to save a few bucks.
EDIT: The more I think about this, the more important I think it is. I understand the underlying issues with the cost of search, but that shouldn't be the dead-end argument. Making ad-free quality search a privilege of rich white people (globally speaking) can't be the answer to this.