[PC] Steam - Sid Meier's Civilization VI - $12.99 US (~$19.99) or $11.04 US (~$16.97) if paying with cryptocurrency - Indiegala

While not the all-time lowest price for this game, this is close to it and definitely the best price around at this time.
The base game has more than enough content to keep you busy for hundreds of hours while of course there is a also plenty of DLC around for the game.
Some of the DLC is also for sale there (same 15% extra off if paying with supported cryptocurrency.) - just scroll down the page a bit and you will see the DLCs.

From the website:

Sid Meier’s Civilization VI, winner of 15 E3 awards including Best PC Game and Best Strategy Game, is the next entry in the popular Civilization franchise, which has sold in over 35 million units worldwide, including more than 8 million units of Civilization V.

Originally created by legendary game designer Sid Meier, Civilization is a turn-based strategy game in which you attempt to build an empire to stand the test of time. Become Ruler of the World by establishing and leading a civilization from the Stone Age to the Information Age. Wage war, conduct diplomacy, advance your culture, and go head-to-head with history’s greatest leaders as you attempt to build the greatest civilization the world has ever known.

Civilization VI offers new ways to engage with your world: cities now physically expand across the map, active research in technology and culture unlocks new potential, and competing leaders will pursue their own agendas based on their historical traits as you race for one of five ways to achieve victory in the game.

Key Features

EXPANSIVE EMPIRES:

See the marvels of your empire spread across the map like never before. Each city spans multiple tiles so you can custom build your cities to take full advantage of the local terrain.

ACTIVE RESEARCH:

Unlock boosts that speed your civilization’s progress through history. To advance more quickly, use your units to actively explore, develop your environment, and discover new cultures.

DYNAMIC DIPLOMACY:

Interactions with other civilizations change over the course of the game, from primitive first interactions where conflict is a fact of life, to late game alliances and negotiations.

COMBINED ARMS:

Expanding on the “one unit per tile” design, support units can now be embedded with other units, like anti-tank support with infantry, or a warrior with settlers. Similar units can also be combined to form powerful “Corps” units.

ENHANCED MULTIPLAYER:

In addition to traditional multiplayer modes, cooperate and compete with your friends in a wide variety of situations all designed to be easily completed in a single session.

A CIV FOR ALL PLAYERS:

Civilization VI provides veteran players new ways to build and tune their civilization for the greatest chance of success. New tutorial systems introduce new players to the underlying concepts so they can easily get started.

Enjoy!