NASA loves to downplay expectations in case something goes wrong, but people really underappreciate just how overengineered these things are, which makes sense when a bad mission can be political suicide for their future funding.
NASA says the voyager mission cost 865 million dollars from the start in 1972 to Neptune encounter in 1989, and currently runs at 7 mllion dollars per year.
(based on number of taxpayers in 1989 -- using the numbers from 1972, it would be a low double-digit amount).