BOOM video 4082
As mentioned, the 'Bonfire of the Vanities' DLC comes in two flavors. The "vanilla" variety will cost 320 Microsoft Points ($4), and includes the main story expansion set in a new district of Florence, wherein protagonist Ezio joins forces with Machiavelli to take down the mad monk Savonarola.
Another, slightly more expensive version of the DLC includes the aforementioned story expansion, plus three new explorable locations. The "enhanced" version of the DLC will cost 520 Microsoft Points ($6.50), and the extra locations are detailed below:
Palazzo Medici - Located in Florence, the player gets to explore the house of the Medici family. It is located in the San Marco district of Florence.
Santa Maria dei Frari - Located in Venice, in the San Polo district, the player gets to explore this renowned church built in the XIIIth [sic] century.
Arsenal Shipyard - Venice was known for its Arsenal, a shipyard that was settled in the eastern part of the city. The last Templars' Lair is located there, and lets the player explore the Drydocks.