Currency

Coins of copper, silver and gold are the currency used in George R.R Martin's A Song of Ice and Fire series although some cultures in it rely on it solely for barter, and in some cities, slaves are a medium of exchange.

In Westeros
Seven Kingdoms -

Coins are used in the Seven Kingdoms, chiefly Gold Dragon's Silver Stags, and Copper Stars and Pennies. Gold Dragons are used mostly by rich merchants and noble Lords and Ladies, while smallfolk tend to exchange copper and silver coins and barter is common in rural areas among the smallfolk and up along the Wall.

The current currency was established shortly after the unification of the Seven Kingdoms following the War of Conquest and was used though the whole Targaryen rule and continued through and after the Reign of the Usurper. The king's coinage is one of the most visible manifestations of royal authority. The minting of the coins, exchange rates, and like matters are overseen by the Master of Coin.

Gold Dragons bear the face of the king whose time they were minted in, as well as his name. While house Targaryen reigns, the reverse bore the three headed dragon. Although silver Stags are known for the stag they bear, they were in use during the time of the Hedge Knight, eighty years before Robert Baratheon's coronation. Copper pennies usually bore the Seven-pointed Star associated with the Faith of the Seven.

According to Semi-Cannon sources: Penny and Half Penny.
 * Copper Coins

Half Groat, 2 pennies

Groat, 4 pennies,

Star, 8 pennies, Stag, 7 stars of 56 pennies,
 * Silver Coins

Moon, 49 stars or 392 pennies, 30 moons, 210 stags or 11,760 pennies.
 * Gold Coins

In the Tales of Westeros Roleplay, we're going with this.

A Gold Dragon = 800-1000 $ (Just Being Thought Of)

On the Iron Islands
They pay the Iron Price, taking what is theirs with force.