@V0ldek You missed maintenance and logistics. Military gear is typically amortized over a 30 year period, so a £3M missile might actually cost something like £0.3M to build then a bit under £100K per year to keep in working order (new batteries and motors, regular inspections and refurb, cost of the leak-proof warehouse it's stored in, etc).

it gets expensive because things that modern ashm has to do can get pretty complex. it can go like this: lauch from tube, pop wings open, start jet engine, get to cruise speed and maintain altitude 2m above water. then get to area guided by gps, but you can't just rely on gps only. then get up, start scanning what's forward with its own radar, when target is found dive to it. or fire up additional terminal rocket engine to get to mach 2 or whatever to make intercept harder (that's what one chinese missile does). or launch 7 or so, get them all to communicate, one flies high above and uses its own radar to find targets and guide the rest of missiles. that one up is visible to radars (above radar horizon) so it can get shot down, but that's no problem because if that happens another missile gets up and does the same thing (that's a soviet ashm, can't remember which one). or missile can stay down and communicate with friendly AWACS or nearby F-35 or something to guide it. there are more options

explosive is something like 20$/kg, rocket propellant (if used) would be somewhere in the same ballpark. it's cruise missile so another big cost will be small jet engine, electronics are a bulk of the cost, yeah. electronics are also what is responsible for bunch of new capabilities. new seekers? TERCOM (not on sea but yknow), maybe datalink? camera to feed image back to operator? good inertial guidance can get pricey. harden it all against jamming and EMP, keep all pieces non-chinese and assembled in usa, keep paper trail and things get expensive. and it all needs software too, and software has to be kept classified, so all devs have to have clearance

for 155mm artillery shell something like third of the cost is fuze, with second most expensive component being casing (30kg-ish piece of steel rather precisely machined on lathe and heat treated in specific way)

javelin atgm is like quarter million dollars, and the only thing it has is IR seeker + inertial guidance. it also doesn't keep actual software onboard until launched