Part of it is the sophistication. Take the Tomahawk: assumed range of ~1000 miles , estimated accuracy of 30 feet. Can launch from above or below water. Etc.

The other part is the limited production runs. Until last month, the DoD was generally purchasing ~100 of these annually. There's no scale economy in making these, so those 100 missiles need to support the entire production & R&D of the product.