[@Duck]

It's actually mentioned in the character sheet example when we were rolling for starting currency. To Quote it

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For simplicity's sake, we're doing 3 types of coinage. Royals (Gold), Lordlings (Silver), and Commons (Copper). They each measure 20 of the previous coinage. 20 Lordlings makes a Royal and 20 Commons makes a Lordling.
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Unless you're more so asking for the relative cost of goods like a meal or hireling, then I leave that to Poohead to give us a better idea.