Complex sentence: Its defense installations had cost the U.S. government more than $150 million, which did not include the expense of fortifying the neighboring islands of Caballo, Carabao, and El Fraile.
Split into simpler sentences: Its defense installations had cost the U.S. government more than 150 million dollars. This amount did not include the expenditure for fortifying the neighboring islands of Caballo, Carabao, and El Fraile.