If I would like to take a domestic flight from Haikou to Beijing. what will be the cost like?

Hey, the air ticket fare varies a lot from season to season, so the cost depends on your travel date. Anyway, I can tell you that the fare in reccent days - CNY1400(US$226) - CNY1960(US$316) for your reference. For more info, you can search the flight page of this website.