D:OS EE was on sale leading up to the D:OS 2 Early Access release, and presumably will be again.
Divine Divinity was pretty much given away with the release of Divinity 2 Developer's Cut on GOG (PWYW, 1 cent minimum), and has been part of other giveaways (including D:OS pre-order bonus on GOG) and very steep discounts. Divine Divinity and Beyond Divinity are part of the bonuses in the Collector's Edition of D:OS EE. Divinity 2 was given away as part of some promotions for D:OS 2 at PAX.
