Coles Pyrmont NSW has the Underbelly - A Tale of Two Cities book for $5. I've seen in a few shops (Angus & Robertson, Dymocks) selling this title for between $15-$25.
I picked one up myself. If needed, i can go back to take a picture of the tag. Not sure if this is applicable in other Coles stores in NSW or any other state. Unfortunately, cannot verify when this deal expires but i imagine while stocks last.
At last count, there were at least 15 remaining.
As an aside, in my opinion this Underbelly is nowhere near as good as the first one. Nothing has happened in weeks and I think they're really stretching to make this (uneventful) story last for the full season.
Ep 3 They're trafficking in Heroin.
Ep 4 They're still trafficking in Heroin.
Ep 5 They're trafficking in Heroin and someone gets killed.
Ep 6 They're still trafficking in Heroin but someone has lost their car keys.
Ep 7 Found them again.
Ep 8 They're trafficking in Heroin.