Israel will get the F-35 for nothing, because the USA has already set aside the US military aid money for Israel to "purchase" this fighter i.e. Israel will be "paying" for this plane using money supplied to it by the US taxpayer. That's one of the reasons why the Americans are peeved by this Israeli demand i.e. this is a way for Israel to siphon off that US aid money and spend it inside Israel, instead of inside the USA (where it is meant to be spent). Israel is attempting to pocket billions of US taxpayer funded dollars, and the Pentagon is right to be miffed about it.
Syrian rebels call for regional alliance against Russia and Iran (Reuters)
from the article: U.S. may allow Israeli upgrades to F-35 fighter jet