Cheap Gold Coins

In Real Life gold coins were like hundred-dollar bills; only used for very large transactions, and most people were unlikely to see very many in their lifetimes. But in many fantasy settings the most basic equipment costs dozens or even hundreds of gold pieces.

This is most likely to give players some point of familiarity by making the cost similar to what it would be in dollars, or yen in Japanese games (which might be why they tend to be worse with it, as the yen is currently worth about $0.01).

For a basis of comparison, a "cheap sword for a peasant" cost six pence (1/40th of a pound) in the 1340s. In the 14th century an unskilled or semiskilled laborer working for wages-only would have earned around 1 to 2 pounds per year (a servant working for board plus wages might have earned as little as two shillings - a tenth of a pound). A middle-class urban family might earn 5-10 pounds per year. The most common gold coins of the era were worth around six shillings (a bit under a third of a pound) or more, so for most people, one (generic) gold coin would represent at least a few weeks' earnings, if not a few months'. You would not use gold to do your grocery shopping.

Contrast Ridiculous Future Inflation. Compare Worthless Yellow Rocks. See also Gold-Silver-Copper Standard.

Anime & Manga

 * Averted in Spice and Wolf, where in one episode Lawrence has to exchange his gold coins for silver in order to buy clothing (the vendors wouldn't have change). Also one of the early plot arcs involves speculation on the silver content of one nation's coins.

Comicbooks

 * Cerebus the Aardvark: Averted, in that Cerebus is able to buy room and board at an inn for the rest of his natural life with a single gold coin.

Literature

 * Mainly averted in Discworld, where the "gold coins" issued by the Ankh-Morpork banks actually contain less gold than seawater. Justified in the Agatean Empire (the fantasy counterpart to Imperial China), where gold is a very common metal and is used for low-value coins. Played with when the first Agatean tourist arrives in Ankh-Morpork with a chest full of pure gold coins, and starts paying for meals with enough gold to buy the restaurant, forcing the Ankh-Morporkian authorities to react to the threat to the economy.
 * Parodied in Myth Adventures, Skeeve and Aahz are given a pitiful amount (on Klod) of gold coins to win a war with, but on Deva it turns out that one gold coin is a pretty decent asking price for an interdimensional mercenary's services.

Live Action TV

 * Averted in an episode of the Babylon 5 follow-up Crusade; the crew visits a human colony which is voluntarily living at a pre-industrial level. Captain Gideon goes to a tavern and holds up a gold-colored coin, asking for whatever it will buy. The tavernkeeper responds that it's enough to buy the entire tavern. Not just all the food and drink in it. All of it.

Tabletop Game

 * Dungeons and Dragons:
 * A simple dagger costs two gold pieces. According to the Player's Handbook v.3.5 gold pieces are a third of an ounce. The current price of gold is over $1600 per ounce, which means that a simple dagger is worth about a grand.
 * It was worse in 1st Edition, wherein a gold piece weighed a tenth of a pound (about 1.5 Troy ounces). And a simple dagger still cost two gold pieces.
 * In 1st Edition the widespread use of gold coins was explained in the Dungeon Master's Guide as being a result of "gold rush" economics. Adventurers were constantly going out and raiding lost tombs and monster hoards, bringing back the gold they found and spending it. This led to serious inflation and a significant decrease in the value of gold.
 * Which is handled fairly realistically in this Nodwick comic.
 * Goblins once parodied the poorly thought out prices in the Player's Handbook.
 * Previews for the fifth edition have claimed it will avert this, basing prices in silver instead of gold.
 * Averted in GURPS Dungeon crawl adventures. A copper piece is worth about a dollar, while a gold coin is closer to $80.

Videogame

 * The Elder Scrolls series in general. In Skyrim, one merchant mentions that with the dragon attacks supply routes are cut off and he can charge almost anything.
 * Gold pieces are Runescape's standard Global Currency. A typical tavern might charge one or two gold pieces for a mug of beer. A chocolate cake is about 400 gold pieces. A typical piece of armour could be anywhere from 40,000 to 20,000,000. A pumpkin costs hundreds of millions.
 * Almost averted in Dragon Age, where one gold coin equals 100 silver coins or 10,000 copper coins. IRL, the respective metals' prices ratio is about 427:8:1. However, a standard dagger costs 8 silvers in Origins and 5s 24c in II, which is about five bucks by the same calculation as used in the D&D example above.
 * Nethack: A fortune cookie costs 7 gold zorkmids, a food ration 45 zorkmids, and artifact weapons cost a few thousand zorkmids. Back-calculation from the weight system suggests that a zorkmid weighs about 40 grams, or about one and a quarter troy ounces. In the last 10 years, Real Life gold has varied between approximately $200 and $2000 per troy ounce, so that's $1,750-$17,500 for the fortune cookie, $11,250-$112,500 for the food ration, and a cool million or ten for Excalibur.
 * The Ultima series is an odd case with this. The existence of silver and copper coins in the game world is mentioned, but you only ever see gold yourself. A person working at the mint in Ultima VI shows you copper and silver coins, and then says something like "A grand adventurer such as yourself would surely only deal in gold." That still doesn't explain why one night at a regular inn can cost twenty gold.
 * Castlevania: The absolute cheapest, most worthless crap goes for 100 gold.
 * Dungeons and Dragons Online is even worse than the tabletop game, instead of ten silver to one gold and ten coppers to one silver each denomination is worth a hundred of the previous coin.
 * In Diablo II and III, a gold piece is the tiniest unit of currency in the game. Level 1 monsters routinely carry up to 10 gold pieces (which they drop on the ground when you kill them). Vendors are willing to pay you 2 gold pieces for a damaged club (basically a broken stick). By level 10, you'll be carrying around (and paying) thousands of gold pieces.