Wow, Time Warner fails at their job for a day or two and you guys come back with complete monetary systems! The awesome here knows no bounds.
To answer one comment, yes basically everyone will be using magic "currency" though I dont like the term. It's more about having a commodity-based money, since they arent "minted" in the traditional sense, but are used up. Picture common towns as looking something like the old west; any manufactured good like a pocket-watch or fancy kitchen tool would instead be some magical gizmo equivalent. In the case of the pocket-watch, "modern" clocks for them are enchanted sticks of varying sizes (finger sized for pocket-watch up to building sized Clock-pillars) that glow different colors and shift a line up and down, as a throwback to when all their time measurement was bases on standardized Candles with graduated markings to tick of hours and minutes (as opposed to our round clock faces that are Sun-dial descended). Fancy ones might have a small magical light dispay (safe), when ancient ones would embed fireworks in the wax, but this is basically a cookoo clock equivalent. But magic stoves and lanterns and other common household items would be the norm at all levels of society, though of course the high-society will have to display more extravagance.
What I pictured was that each of the 4 elements had an energy that could be stored in mundane objects (in a straightforward process by nearly anyone), as everyone has what it takes to use basic magic, even if they dont have the talent and/or skills for advanced work. In terms of value they would each occupy a different order of magnitude of currency, but in a way that would be a physical-law conservation-of-energy sort of exchange, rather than a regulated/floating value. So it would take so many Sparks (fire denomination, equivalent to a unit measurement of thermal energy) to equal one Stone (Earth denomination) because it take exactly that many units of Fire Magic to generate that single unit of Earth Magic. Im thinking Fire/Water/Earth would be the Low/Middle/High values; Ill leave Air as a more exotic item, since anyone can imbue Breaths (but they are of miniscule relative value), but it is astronomically more difficult to contain and store permanently, so it's rarely done. When it is, it's generally considered an extravagant show of wealth, and the pursuit of a way to store Air is like the medieval search for Gold from Lead widely viewed as a would-be Game-Changer for the society since it could be the key to things like weather manipulation and easy sea travel, even the holy grail of Flight-for-the-Masses.
My current concerns about all this are:
1)How does a commodity-based currency work? I know destroying minted currency devalues it, but what if it was intended to be Used Up from the get-go? How did it work way back in the day when Salt was a standard of trade?
2)Is it safe to leave it directly tied to the effort of empowering? It prevents a need for regulated currency, and counterfeiting wouldn't be much of an issue with properly defined and common measuring tools. But it does establish a direct monetary value for /effort/, which seems like it would have broad implications, as it could take bargaining for wages all but non-existent, and anyone could just sit river-side and churn out money to the limit of the containers they could beg/borrow/steal
3)Should I instead force the standardized currency to be issued by one of the guilds? It could be a useful story detail for the political interplay of the world, if one of them is in charge of the Currency. Perhaps anyone can technically empower a bucket of water, but to do it properly requires a larger volume than is practical outside of an organization? Counter-fitting still wouldnt be too much of an issue since they'd still have an objective value in their energy content.
4)Should purity of the container be an issue? It would make sense if pure water held energy more efficiently than a mud-puddle, and I could see different gems holding a different amount. But I want it to focus on the energy as the Money, and the Gem/Water/whatever physical object being viewed more along the lines of a disposable purse.
5)What am I not even thinking of, because I dont know enough about how economies function?