Once you have an army of robot slaves ... you've rendered the whole concept of money irrelevant. Your skynet just barters rare earth metals with other skynets and your robot slaves furnish your desired lifestyle as best they can given the amount of rare earth metals your skynet can get its hands on. Or maybe a better skynet / slave army kills your skynet / slave army, but tough tits, sucks to be you and rules to be whoever's skynet killed yours.