> The relative financial cost to the enemy is almost irrelevant if they are much wealthier than you are.

The cost is often proportional to the cost and complexity of making the item.

Yes I oversimplified, but it helps to put into context the cost delta of a patriot and a mini shahed.

Logistics, logistics logistics. Diversity of manufacturing location and suppliers.

Right now for example the US has 1-2 suppliers (and sometimes it's just another sub company) for critical weapon parts.