Even though people's intuitions do lead them to believe it is morally necessary for one to save the hypothetical drowning child, in that particular scenario, I wager that there are situations in which people's intuitions would lead to other conclusions. One relevant hypothetical scenario is one in which one is amidst a group of people who also are observing the drowning child, and who are better able to bear the economic hardship of losing a pair of dress shoes (I know that the phrase "economic hardship" sounds rather callous in this scenario, but I cannot think of a better phrase off the top of my head.) Hell, perhaps some of them own thousands of pairs, while you own only one pair.

I guess what I am trying to say is that I have a pet theory that people's objections to Singer's scenario, whether they know it or not, are largely game-theoretical. In light of this, I see debates over the the precise cost of a child-saving as being, not irrelevant, but at have little to do with a much more important objection to Singer's argument.