Between sales, the price of Civilization V on Steam is $49.99. The total cost for “All Downloadable Content For This Game” is $49.39.
When DDO came out, I wondered why it was not using a module pricing strategy: base game cheap/free, sell the dungeons individually. You could even have a store for player-made, developer-checked dungeons for which players get a cut. Of course, selling the packs piecemeal encourages power creep by the question of whether this pack is worth the $5. Is the Mausoleum of Halicarnassus awesome enough to spend extra money on it? The same power creep/worth it question arises every time Team Fortress 2 puts a new weapon in the store, but at least there you face a near-certainty of getting the weapon as a drop (or crafting it) fairly soon.