Your oversimplification bakes in too many assumptions.
The relative financial cost to the enemy is almost irrelevant if they are much wealthier than you are.
What matters most is the intangible military value of the item.
In too many situations people think simplistically about dollars, when what matters is invisible or intangible values. The hyperfocus on money is especially egregious among people that don't have much.
> 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.