All credit to
Right now, you can get Sleeping Dogs for as little as £4 via Greenmangaming.
"GMG has Sleeping Dogs for 66% off at the moment (product key redeemable on Steam) AND you can use the current 30% voucher, too.
Just insert that in the little voucher slot at checkout."
Note. Before purchase, you'll be given the option of credit or cashback. Taking the credit option nets you £4 for future purchases, cashback deducts a further £3.