Should be easy to rent a cell phone at the airport. I know at Pudong in Shanghai to the
right of the international exit area there is a cell phone rental booth/place.
I bought a couple re-fill cards from them. The prices are pretty cheap for rental.
Now there are a lot of used cell phones for sale in China at cheap prices so you could probably buy a cell phone and a sim card with time on it for less than $40.
That's an option.
Then you have an unlocked GDM phone you can use in other places.