The Price of Life and Peter Singer

What is a life worth? It is difficult to understand what this question even asks. Does it ask; What kind of thing, or what amount of a certain kind of thing, could satisfactorily replace a human life? This does not clarify the original question so much as point out what it is that makes it initially so hard to grasp. That is, it is implicit in the question that it is possible that a life can be ‘worth’ something at all which, taken in the sense of a given life being replaceable by something of commensurate value, appears to be a mistaken assumption. Or is the second question just misleadingly worded? If we were to ask instead what kind of thing a life is worth giving up for, then the possible contexts in which one might be inclined to agree that the loss of a life can be justified by the certain good that it may bring about begin to come to mind.