And the price is rock botton. you can have a simple one that can cool a small to medium room for about 200$ and a bigger one for the main room is about 500-700$. installation is usually another 150$. 4200$?? - crazy.
These are placed in the yard away from the house. Here's a picture: http://www.getgreenair.com/wp-content/uploads/2011/03/home_h...
The point is if you can't afford to spend $4K on air conditioning, $600 might be within the budget.
Also I'm not sure central one is more efficient. it cools entire house while using individual units you can cool just one room. Of course it has the capability to limit the airflow per room etc, but I'd guess most people don't do that and just cool/head the entire house.
My time in Israel was rather cold and required a jacket most times :)