Normally, From time to time, the HKG (Hong Kong) to PVG (Shanghai Pudong) has special price tickets available.
I just reserved the China Eastern Airline tickets (MU) for next Tue to Shanghai and return.
It costs only HKD1300 and totally around HKD1750 include the tax.
For Dragon Air, they alway has special price ticket available on internet. You may check with its website or register for the e-mail alert on it to receive the updated information.
For the ticket between Shenzhen and Shanghai, they also have promotion tickets from time to time. The cheapest price start from CNY 3XX (one-way only) + 130 tax etc. You may check with eLong or Ctrip.com for the ticket information.