SuperPheemy

The Guild Empire, because of it's economic strength due to it's ability to draw upon the resources of seven worlds has the luxury of controlling the value of its own currency. Thus, in Guildspace, only Guild Minted currency is legal tender. The Empire, to shepherd it's supply of precious metals like Platinum and Gold enforces a Silver standard economy. Which means that items within the Empire are measured in silver where the value of the same item outside of the Empire is measured in gold. This leads to a second-tier of exchange in those worlds with regular contact and exchange with the Guild Empire. Zhor-Shant for example. Guild Coins in these border regions are more valuable than their metallic weight would otherwise indicate.

To start, the currency minted by the Guild Empire is as follows (from most valuable to least).
Platinum Great Wyrm (PGW)
Gold Wyrm (GW)
Silver Drake (SD)
Copper Wyrmling (CW)
Bronze Drakeling (BD)

1 Platinum Great Wyrm = 24 Gold Wyrms
1 Gold Wyrm = 6 Silver Drakes
1 Silver Drake = 12 Copper Wyrmlings
1 Copper Wyrmling = 24 Bronze Drakelings

Outside of Guildspace, interworld trade continues to measure value based on a coin's metallic value. Most ports that engage in interworld trade hold to these exchange rates (though depending on local economic conditions, these rates may vary).

From most valuable to least..
Platinum Coin (pc)
Gold Coin (gc)
Electrum Coin (ec)
Silver Coin (sc)
Copper Coin (cc)

1 Platinum Coin = 6 Gold Coins
1 Gold Coin = 4 Electrum Coins
1 Electrum Coin = 3 Silver Coins
1 Silver Coin = 24 Copper Coins.

In the worlds near the Guild Empire, Silver Drakes are valued the same as Gold Coins. Which leads to the following value chart
1 PGW = 24 GW
1 GW = 6 SD = 1 pc = 6 gc
1 SD = 12 CW = 1 gc = 4 ec = 12 sc
1 CW = 24 BD = 1 sc = 24 cc

These are raw value charts, literally how a character might calculate the value of their coinage. But the only valid currency in the Guild Empire is Guild Coin. Thus the Empire levies a 25% tax on all foreign coin exchanged for Guild Coin. Furthermore, Moneychangers are regulated to charge up to a 12% fee (which nearly all do, Moneychangers gotta make a living too) on all transactions.

Outside of the Guild Empire, reputable Moneychangers charge fees anywhere from 10-30%. However, Guild Coinage is usually valuable enough that most moneychangers will only charge a 10% fee. This is because Guild Coin in these ports are actually purchased at a rate 25% above their normal value.

This means that an "honest tradesman" with 100 gc, can change those coins into 63 SD in Guildspace (100 gc = 100 SD - 25 SD in tax - 12 SD in fees)

That same tradesman in Torcosia with 100 SD can change those coins to 112 gc and 6 sc (100 SD = 100 gc + 25gc markup - 12 gc, 6 sc in fees). Note no taxes in Torcosia ("honest tradesmen" HATE taxes).

Another tradesman in Torcosia looking to buy those 100 SD will be charged 125 gc for them (assuming the moneylender is willing to sell of course). Thus the Moneylender makes a clean 12 gc and 6 sc buying and selling Guild Coin. Or in economic language, our Moneylender has turned a tidy 12 1/2% profit.

Hopefully, this all makes some form of sense. For those of you mathematically inclined, I invite you to critique and possibly break this exchange system.