Some of the costs are hidden. The Neptune missile was cheap. The hidden, often unaccounted for part of that system however are the ISR (Intelligence, Surveillan

Some of the costs are hidden. The Neptune missile was cheap. The hidden, often unaccounted for part of that system however are the ISR (Intelligence, Surveillance, and Reconnaissance) capabilities to find the target. Anti-Ship missiles (AShMs) like the Neptune and practically any others have a limited ability to see what's around them because of the altitude they fly at and the overall small frame for radar power. This means the operator has to identify where the ship is, where it's going, and then fire their missiles to intercept. There's practically no communication afterwards (certainly not in Neptune's case) so the further away the ship it, the greater the chances it will move in that time and the missiles will fail to acquire it. (Firing closer as you can imagine brings its own risks.) So you need a system or system of systems to find your target, relay that information down to your launchers (securely, quietly, and timely!) so you can launch your relatively cheap weapon. That's where all of the investment in communications, radars, overhead platforms (drones, aircraft, satellites) comes into play. The GlobalHawk that had been flying over the Black Sea for weeks at 40,000 feet isn't cheap, but without one, one's firing missiles blind. The further out you get, the more eyes and links you need to find and track your target, and that's where it gets expensive. It also becomes less of a sure bet.