It's not just the economic cost that is a consideration here. The military applications of AI are potentially staggering (as are the associated ethical concerns - but, as with any military tech, once someone does it and the advantages become clear, others will inevitably follow). No major power player is going to want to risk getting drastically outpaced by its primary competitors.

Note that this isn't a hypothetical, either. Israel is already using AI to pick targets. Ukraine is already using AI-controlled drones to beat jamming. There's no indication that either one intends to stop anytime soon, which tells the others that the tech is working for this purpose.