Why Obama's 28 helicopter cost 11.2 billion dollars.

Obama's helicopter would cost 400 million dollar each, because this helicopter is not just a helicopter, according to Washington Post this helicopters are equipped with cutting-edge communications equipment, antimissile defenses and others.

And Why Obama needs 28 helicopters?

It's for safety purposes, that when flying with identical helicopters, bad guys will be confused, which of this is the president's ride.