China visa extend in Shanghai.

Hi .
I travel to Shanghai by cruise ship and use my 144 hours China twov exemption under China policy. I have only 4 hours to fight out of Shanghai transit to Hongkong then to home Sydney; just in case if my fight cancel or delay . Is it hard to apply China visa in Shanghai, how soon i can my China entry permit and the cost?
This is my first time in China. Thank you for reply.
Lyn from Australia.