Is this a lot? Missiles are quite expensive in general. $3.8 BN is not the budget for this single program, but for several, 8 per this source [1] (although, now it might be 1 or 2 less).
For this particular weapon, a somewhat similar weapon I can think of is the European Meteor [2], which is ramjet (rather than scramjet) powered, and reaches Mach 4, rather than over Mach 5 as this one is supposed to do. Meteor comes at a cool cost of EUR 2 MM per piece. Think about it, you fire one missile like that, and it's like destroying 10 Ferraris.
