Your 'truth' forgets that most Qassams (close to 99%) end in the desert. That means only one Iron Dome missile will be fired for every 100 Qassam. So that a 'successful' Qassam costs $10000, something Palestinians can afford even less than Israelis before they go totally bankrupt. Besides each Qassam is a war crime since it is not able to reach a military target. So not only they would lose the money war, but also the opinion war. Since they are already considered as terrorists, by the states, they cannot afford losing that much.
Iraqi police fire tear gas as thousands of protests burst into Green Zone, storm Parliament (AP)
from the article: MESS Report / Iron Dome passes tests, but how much will it cost Israel?