$500 per 16 inch shell... Maybe in 1945 dollars (does it include the propellant cost?).
Currently the regular 5 inch shell (plus propellant, shell is no good without it) costs more than $500. If they were still producing 16 inch rounds, I’d expect them to be a bit more expensive than 2000 pound bombs.
Most likely 1945 dollars, as they didn’t crank up production lines again. Also, they made hundreds of thousands if not millions of them in WW2. Economies of scale and all.
But even so, a Mk84’s (2000lb dumb bomb) per unit cost was $3100 back in 2000, not exactly a lot worse compared to literally any guided missile. Even adding a Paveway guidance package to the dumb bomb only adds ~$25K to it.