BOM cost falls when every line earns its place.

You reduce it by deleting lines that do no work, by buying catalogue parts at the quantity you will actually place, and by refusing variants that split that quantity into piles too small to purchase well. You do not reduce it by typing a lower price over a part that misses the rating, the footprint, or the second source you were quietly depending on.

Geometry, bare-board fabrication and the choice of a silicon each deserve their own review. This article is the structure of the list: custom versus catalogue, minimum order, alternates, cables, packaging, and the unit cost you only get if every line arrives in the same week.