Wiki says that $800M gives you a battery of 6 launchers (each equipped with 8 missiles), 2 tactical centers and 1 radar. So the upper bound for one missile is 1

Wiki says that $800M gives you a battery of 6 launchers (each equipped with 8 missiles), 2 tactical centers and 1 radar. So the upper bound for one missile is 16M. Still very expensive of course, but not 100M expensive.