Yeah I can't figure out why this is, exactly. If batteries are such a huge cost center, why can't I save a significant chunk of change by opting for a vehicle that has 100 or 200 miles less range?

I'm not quite up to date what LFP batteries cost nowadays, but I remember it's in the $70ish range - so for a respectable 80kWh, it'd only cost $5.6k out of the total. Considering you can get something like a new Corolla for $20k-ish, if the EV minus battery costs the same as a fully fledged ICE car, you could have a $25-27k car with a quite generous battery.

You can? Going from the 84kwh ID3 to the 55 kwh saves you around 17%