How much is double-entry chinese visa ?

I am going on a 14 day cruise with Princess Cruises and I am required to get a double-entry permit - I am a dual citizen - U.S. & Philippines and I have both U.S. & Philippine Passports. Which passport is advisable to use? By the way I already booked my ticket originating in the Philippines and coming back in the Philippines - Manila to Beijing and HongKong to Manila for return.