Though I don't think it needs to drop exponentially. Take any of the new EV (Leaf, Bolt, Model 3) that are $35k and drop the price by 2/3, keep the 200 mile range, and ICE car sales will die fast. ICE car prices are not dropping. EV only need to drop below ICE, not a continuous Moore's law.
I bought a used 2015 Leaf recently for $8500. Yes, it's only 80 mile range, but that gets me to work for two days without charging. It's nearly free to drive; $0.02/mile energy costs, or nothing if I charge for free at local charge stations.
There's the flipside to consider too: ICE car prices are as low as they are today because of huge efficiencies of scale in existing engine supply chains and also a large inventory of used cars. Used car inventory is something that will market align over time. Engine supply chain disruptions are hard to predict, but can snowball quickly.
I bought a used 2015 Leaf recently for $8500. Yes, it's only 80 mile range, but that gets me to work for two days without charging. It's nearly free to drive; $0.02/mile energy costs, or nothing if I charge for free at local charge stations.