So, I gather that money systems in D&D is on a par with, say, near lightspeed rocks and jump torpedoes in Traveller: OOOO-VEERRRR discussed. Ooops. Well, if its any consolation, rest assured that I could be writing screeds about planetary atmospheres and empty hex jumps with jump torpedoes, so consider that I'm not doing that to be a win for now.
So, There's bunches of theories about how to organize faux-medieval money and economies: the ale standard, the lunch standard, the cow standard, the biblical standard, the standards of Diocletian, the wereguild standard, and more. And, obviously, they all disagree, 'cause the very meaning of money now is different now from what it was then, and often from what it was in the time we are trying to emulate relative to the time we have references for.
Throw in the fact that back then our fluid metal rates didn't exist, and that there was no use for silver and gold other than coins, bullion and jewlery, and so even the value of them doesn't mean what it used to, and there's no way for a hobbyist, even an obsessive one, to untangle it.
And, then, the whole slavery thing: a slaveholding society is going to mess crap up far more than one can imagine. See, there's this class of workers where most of the expense is up front (and cyclically very cheap) , and the daily wage is just for food for them. The point is, even the value of a days labor cannot be used to value items: what is the real value of a sword when made by slaves vs made by a (not enslaved) blacksmith. Hard to say.
So, why the droning about economics ? Becuase I'm building a rationale for doing it my way and ignoring unsightly contradictions, thats why.
Some few facts that seem to emerge from the morass can be used to gain a grasp on the subject for RPG purposes.
1. Silver < Gold, almost always.
2. Food < crafted goods, almost always.
3. Clothing is surprisingly expensive, actually: Hardware can be industrialized far more efficiently than clothing production.
4. prices change, but basically ratios give a clearer illusion of consistency.
5. A standard days pay should keep you from starving or eating your children. Slavery messes with this, seriously.