We all know that an extra dollar is worth more to you the poorer you are. That's why it can be good to donate money to an organisation like GiveDirectly even when a few cents in the dollar get used up in transaction costs. But how much more is it worth? Economists have a good quantitative model of what is going on, which can enable us to make rough comparisons about whether, say, people on $1,000 per year would get more value from an extra $100 than people on $2,000 per year would get from $200. This can help us work out how much additional cost we should bear to get money to the very poorest people.
It can also be useful for improving our thinking about the relative values of different financial flows such as remittances and aid. It is easy to find out the sizes of these in dollars, but what about the size in terms of value to the individuals? If the individuals in one case are substantially richer, then this can really change things.
I've written an article explaining how all of this works up on centerforeffectivealtruism.org. Have a read and let me know what you think.
Tengs, et. al. (1994) quotes some cost-effectiveness estimates for a bunch of developed world interventions. The best seems to be anti-smoking campaigns.
Xu, et. al. (2015) finds a US CDC-led antismoking campaign to cost $393 per life year and $268 per QALY. Ratcliffe, Cairns, & Platt (1997) find a Scottish anti-smoking campaign to save a life year for £304-£656 (roughly $742-$1603 in 2016 USD). Stevens, Thorogood, and Kayikki (2002) found a London anti-smoking campaign to cost £33-£391 per life year ($66-$786 in 2016 US dollars).
Apples-to-apples, we could look at anti-smoking campaigns in the developing world, with Savedoff and Alwang (2015), writing for the Center for Global Development, quoting it as $3 - $70 per DALY averted.
Taking these numbers literally, it looks like developing world anti-smoking campaigns are ~20x more cost-effective than developed world anti-smoking campaigns. Other interventions are likely to be even more tilted in favor of the developing world, because they treat important problems that just aren't problems here anymore. Malaria is still a huge problem in Africa, but was eradicated in the US by 1960.
I think that's the best direct comparison I have right now.