That doesn't make sense because the second hand car is not cheaper by the amount of the subsidy. Say subsidy is $20k, second-hand car might eventually be $6k cheaper (and the discount time value of money means that the $6k is actually less than $4k). Giving the wealthy person $20k, and the poor person less than $4k is strange.
New Zealand used car market is likely very different from the market where you are. The cheapest Model 3 I could find was a USD18000 for a 2020.
Subsidies make sense if the environmental gains outweigh the costs of the subsidies.
Subsidies: there was a purchase subsidy, charging stations were subsidised, and I think electric cars are not paying their fair share of road maintenance (much of our road costs are paid for by an excise tax on usage via petrol-tax or heavy-vehicle-milage).
