If dense strategy is what you're after, this Humble Stardock Strategy Bundle is worth a look. For $1 ($1.50 in Australia) you get Fantasy 4X's Sorcerer King: worth it on its own, but you also get Dead Man's Draw, a strategy game featuring pirates. Quite rare.

But if you're keen to pay higher than average, you'll get an avalanche of Galactic Civilizations 3 stuff: the base game plus three expansions including Crusade, Retribution, and Mega Events DLC Bundled together, at the time of writing in 2015, Richard Cobbett wrote that the game "remains by far the best modern way to conquer the unknown universe. At the time of this writing, the price is $10.14 ($16.43 in Australia).

Finally, if you have $13 ($21 in Australia) to spare, you can buy the entire "Star Control" line ("Star Control Origins," "Star Control 1," "Star Control 2," and "Star Control 3," plus the "Galactic Civilizations 3" expansion ( Intrigue"), and "Ashes of the Singularity") can be unlocked: Escalation. Click here for the bundle.