Well, it depends on your utility function, but judging by Zuckerberg's experience with the Foundation for Newark's Future vs. mosquito netting in Africa, I think that ratio is not out of the realm of possibility.
Yes. Consider mosquito nets (<10$) to protect against malaria vs. training a guide dog (~50k).
A $1,000 donation, if given well, can measure better on this metric than a $1 million donation, if given badly. Not a very meaningful thing to say, I agree.
Um yes. There are way more folks in a position to give $1k than $1m.