It’s kind of funny how most of the science fiction and fantasy I’ve read skims over matters of finance. Or maybe not so funny, given that I’ve not run into too many authors who actually get how money works. I will freely admit that my understanding is shallow at best.
At the same time, there are so many opportunities missed by just having some vaguely defined currency unit that every follows, whether said unit be credits (common in science fiction), gold or silver coins (staple of fantasy, although you don’t often see much about the weight of said coins or about shenanigans like degrading gold coins with cheaper metals – and the inflation that follows.
Heck, I’ve wondered what would happen to the Harry Potter universe if a savvy muggleborn took one of those galleons (which cost five pounds sterling each) and sold it to a gold dealer on the muggle side. Rowling implies pretty strongly that the coins are if not pure gold, then damn near, possibly with a few extra enchantments so the coins aren’t too soft. Presumably similar enchantments on sickles and knuts stop the silver and bronze tarnishing.
Just imagine… muggleborn spends 5 pounds. Takes their shiny gold galleon and sells it to a gold dealer. The descriptions suggests a galleon is probably about an ounce, so there’s a good chance that once the dealer takes his cut, they’ll get back say… let’s round it to 200 pounds (which is probably on the cheap side since I’m pulling figures out of my anatomy). Waits a while and takes the 200 pounds to the goblins. Gets 40 galleons. That’s one heck of a return rate, although it would need to be done carefully and not too often to avoid suspicion. Even if there’s some kind of enchantment on the coins, by the time a muggleborn finishes school, there’s a decent chance they’ll be able to remove the enchantment. Or just damage the coin enough that it’s not recognizable as an actual coin.
Money is complicated. It’s not this deep arcane thing, but there are definitely fun quirks a writer can play with. Take today’s tech level. There are numerous currencies in use around the world, most of them fiat currencies, which means a specific denomination is worth more or less what the people using the stuff say it’s worth. Generally speaking the exchange rate between different currencies stays more or less stable, as in one US dollar usually buys a little more than one Canadian dollar, and something less than one pound sterling. The more political and other instability in a country, the more likely its exchange rates will go all over the place (one of the reasons I doubt the Euro will last, as it happens. Countries with chronically unstable politics tend to have wildly fluctuating exchange rates – that rarely if ever come close to parity with the currencies of more stable nations. There’s a reason the Deutschmark was ridiculously stable and high-value before the Euro was created. It’s much the same reason the Lira wasn’t all that stable or valued. Shoving a mixture of stable and barely functioning economies into a single currency isn’t going to work very well).
The same thing is going to happen in any fictional world. What you pay for things will depend on how common they are at the location (you have no idea how long it took me to get over the idea that the lorikeets that form huge wild flocks in South East Queensland are seen as immensely valuable exotics over here in the US. I had the same reaction to finding passionfruit advertised as an exotic tropical fruit, complete with fits of giggles at the thought of the vine that damn near took over the back porch when someone dropped some seeds there being a precious exotic fruit), how difficult it is to produce, and of course, how much people want it.
Which naturally means that if passionfruit vines grow like weeds where you live, they’ll be cheap, but if your climate is totally wrong for them and you’ve got to either grow the things in a carefully monitored greenhouse or import them from somewhere, they’re going to cost a ton and be a status symbol. Since – just to complicated the whole matter of what’s valuable – anything that’s rare and difficult to get hold of is certain to become a status symbol for whatever form of wealth your world has.
This is why I figure that if we ever get to a level of tech where meals can be cheaply synthesized, the prestige eating places will make a big deal of having human cooks and wait staff. Similarly, in a lot of houses built or renovated in the 1930s in Australia, if the owners could afford it they used asbestos panels in the walls and ceilings. It was the big thing and expensive. Wood was “common”.
Then of course you have the potential for fun in a more modern setting in the form of computer glitches, poor programming and the like. How often does it happen that a mistake in making an online payment results in extra charges? How many people carry around multiple forms of payment because they can’t guarantee that wherever they’re going will take the one they prefer?
And of course the big question – how will your character handle something going wrong with his/her/its bank account?