"NASA launches dual satellite moon mission" "The $500-million pair of washing-machine-sized satellites will take almost four months to reach the moon." Why are satellites that expensive/costly?

I understand that there must be a lot of high-tech stuff in those ‘washing-machines’, but $500 million?
Can anyone, who has a little or big knowledge on the subject, explain to me where the costs come from?
NASA Launches GRAIL