Fun fact: Using any other public US AWS region would save 3 million dollars per month!
Aside from that: Using infrequent access storage for the parts of the data which don't get frequently accessed would save a lot and I'm pretty sure at that scale AWS would be happy to discuss possible discounts as well.
Don't think that's disingenuous, if that's what you're implying. Companies that have an exabyte of data usually know how much it's costing them to have it.
Nothing. Any query processing on sufficiently large amounts of data is going to be expensive in time, space, energy, and money, and Amazon doesn't buy custom hardware for this purpose and intends to make a profit doing it so it's going to be even more expensive.
Aside from that: Using infrequent access storage for the parts of the data which don't get frequently accessed would save a lot and I'm pretty sure at that scale AWS would be happy to discuss possible discounts as well.