First, price is dependent on where iPhone come from. iPhone in Shanghai could be smuggled from overseas or Hongkong or could be from China Unicom. China Unicom is official carrier and reseller for iPhone in Shanghai.
So from different channels, price are various. But the current best deal is from China Unicom. If signed with two year contract for their data plan, customers may get iPhone for free. And because of its official status in China, iPhone from them has official warranty in China as well. This makes a lot of fans feel much better than those in gray market.