Mr. Pedatzur, you either know the topic you are discussing, or you don't. If you say you don't then stop throwing around numbers. Israel has a duty to its citizens, to protect them at any cost. While expensive, the defensive shileds are a sine qua non for Israel's existance.
U.S. warns governments, bankers Iran sanctions still in place (Reuters)
from the article: Missile defense systems won't protect Israel