Maybe it's unfair to limit the award to just Steam — other outlets had other sales. This honors Steam for frequent discounts far and above (or below) anyone else and honors the best example in one award. Those Bitty (that's what they're called in my mind) trophies must be expensive.
Civilization IV: the Complete Edition came down to the low, low price of $13.60 (£8.50/€13.60) during the recent winter sales.
It's pricier than some older/casual games available for a song and two peanuts. But it includes two full games and two expansions, and could be the only PC game you need.
I usually dislike strategy games and turn-based anything but Sid Meier's game has robbed me of so much time I may sue if I fail my degree.