Especially on any kind of absolute scale, when the amounts get so large. It's easier if you consider it in relation to other large governmental expenditures. Fox News (which tends to under-estimate war cost, IMO) has estimated the cost of the Iraq war at >$700B. How does the ISS stack up to that in terms of value to the world? Is it worth about 1/7 of that? More? Less? I'm not sure it stacks up as well against every other possible use of $100B, but I'd personally much rather have another 6 space stations than what we've gotten in exchange for our other $600B spent on war.