They clearly wanted to sell him more than Arsenal wanted to buy him. I can just see the conversations:
Ashley - "Arsene now you've lost Sagna - how about the current France RB?"
Arsene - "Ok - what's your price?"
Ashley - "£20Mill"
Arsene - "LOL"
Ashley - "15MILL"
Arsene "You're actually serious?"
Ashley "We've just bought a striker so need to balance the books - £12MILL"
Arsene - "£8MILL"
Ashley - "£11MILL"
Arsene - "£8MILL"
Ashley - "£10MILL"
Arsene - "£8MILL"
Ashley - "Ok - 8 MILL"