What is the first think you need to know about economics?
If your economy has a gold standard, meaning the value of everything is based on how much gold you can trade for it, then **you need to establish the value of a gold piece in your setting** and the most intuitive way to do this is to determine what is fair pay for an honest day's labor. This is how an individual knows what their labor (meaning their skill, knowledge, and time) is worth, and therefore they know how much of their labor they are trading for a meal, a drink, and a room at the inn, or rent. For example, in real world US dollars, federal minimum wage is $7.25/hr. If you earn minimum wager and if a burger and fries costs $7.25, then you know you're trading an hour of your labor for this meal. Actually no, taxes. Nevermind.
You also need to establish the value of other trade goods, like spices, tobacco, wine, wood, cloth, other materials, beasts of burden, land and property, food, drink, etc. That sounds pretty effortful, but it's all based on the idea of how much gold or labor is fair to trade for it.
Data
Let's look at some numbers from chapter 5 of the 5e PHB and Chapter 6 of the 5e DMG (why not 5e?) to get an appreciation of the value of a gold piece to a person in the 5e setting.
1 gp = 10 sp
1 gp = 100 cp
(we can also write these coinage conversions as 1 gp = 10 sp = 100 cp)
An untrained hireling (assume this is an ordinary peasant laborer or servant) earns 2 sp / workday (let's ignore how many hours are in a workday).
A person living a squalid lifestyle spends an average of 1 sp / day on expenses such as food, water, shelter, clothes, etc.
A person living a poor lifestyle spends an average of 2 sp /day on expenses
Note that lifestyle expenses do not explain if the expense is the cost of YOU or the cost of YOU AND YOUR FAMILY.
A night at a poor inn is worth 1 sp (ouch), squalid is 7 cp per night
A gallon of ale costs 2 sp (ouch again), 4 cp per mug (I assume the poor drink really watered down stuff considering they spend 6 cp on "Meals (per day)" per page 158).
A loaf of bread is worth 2 cp.
A "hunk" of cheese is worth 1 sp (ouch! Can I assume this is the equivalent of buying a block of cheese from the grocery store?)
A "chunk" of meat is worth 3 sp (son ova! Can I assume this is the equivalent of picking up a cut of steak or some ground beef at the grocery store?)
(A sandwich must be expensive in faerun. Good thing I don't live there.)
A skilled hireling (assume this is a skilled laborer or tradesman, likely still a member of the peasant class) earns 2 gp / workday
A person living a modest lifestyle spends an average of 1 gp / day on expenses
A person living a comfortable lifestyle spends an average of 2 gp / day on expenses
Analysis
"Rations (1 day)", weighs 2 lbs, although an adventurer only needs 1 lbs of food per day (reference Chapter 8, Adventuring, section Food and Water on page 185), is worth 5 sp. Really think about this one. 5 sp is the same as 50 cp. 50 / 2 is 25. If a chicken costs 2 cp, then you can buy 25 chickens for the price of 1 day of ration. Poor people spend 6 cp on meals per day. 1 day of rations costs 8 times more money than a poor person spends of food per day. Rations which is defined as an allowance of a commodity during a shortage! The 5e books do not give the weight of a chicken, but I googled it and got a result of 5.7 lbs. Let's round down to 5 lbs because the people of faerun aren't using steroids on their chickens. You can buy 5 lbs of food (one chicken) for 2 pieces of copper, or you can buy 2 lbs of food (one days rations which the book describes as jerky, dried fruit, nuts, and effing HARDTACK) for 5 pieces of silver. Someone is being exploited, and I think it's the idiot adventurers. Call it murder-hobo tax.
As an exercise, look at Maintenance Costs table of page 127 of the 5e DMG. An abbey cost 20gp to maintain per day and requires 5 skilled hirelings and 25 untrained hirelings (30 staff). If 5 skilled hirelings worked full workdays, they would earn 2 gp each and cost 10 gp total per day. 25 Untrained hirelings working full workdays earn 2 sp each for a total of 50 sp per day. 50 sp equals 5 gp. The total cost of your staff is 15 gp per day. Where are the other 5 gp of daily maintenance costs going? Well, this table doesn't have a supplies cost, but we can assume supplies may include food and lodgings for the staff because it's common for the staff of an abbey to be a live-in staff.
Chapter 5 of the PHB has a table for Food, Drink, and Lodging. "Meals (per day)" says 3 sp for a modest lifestyle, and 6 cp for a Poor lifestyle. Notice that people living a modest lifestyle spend five times more money on food than the poor. Our abbey has 30 staff. 30 * 3 = 90 sp. That's 9 Gold, so the abbey probably isn't feeding these guys this well. 6 cp * 30 = 180 cp which comes to 1 gold, 8 silver. Sounds better. We still don't know about the other 3 gold, 2 sp cost of daily maintenance.
The same table also says Inn stay (per day) is 7 cp for squalid, 1 sp for poor. We can assume the abbey is not providing inn service for profit, and if the staff is live-in, then laundering beddings and clothes is part of their duties. I would just assume the cost of soap, which is 2 cp, but we can't quantify how much soap is used based on the information in in the PHB, and so we can't say what the total cost of soap is. I'm just going to shrug and throw my hands up at this point. That other 5 gp allows you to assume some loosey-goosey other stuff. It works perfectly well for your pretend elf-game needs, and that's the point.
Conclusion
I think the costs of things given in the 5e books are inconsistent but functional for a game. Most importantly, I can't say prices are intuitive so that I can't intuit the value of any damn thing and I have to look it up. I think it's fair to say people are easily POOR or worse in Faefun. I mean this game doesn't even tell me about EFFING TAXES. Could I do better at designing an economy in my own fictional setting. I think I could, but it would take me as long as it took Tolkein to write his books. I think what would really strains my suspension of disbelief (if I actually cared about economics) is the cost of adventuring rations vs the cost of meals per day for the poor. And you know what, I say 5e a lot, but for all I know these tables could go back to the first edition in the 1970s and maybe they haven't been updated since. I don't know if any of this data is based on real world data, and if so, how much of it is based on real data and how much is arbitrary.
Proposals
Proposal 1. Make all food and drinks cost 1 cp minimum and 2 or 3 cp maximum. Remember a whole chicken is worth 2 cp in the rules. People cannot break money down into amounts smaller than 1 cp without bartering. So, when a restaurant puts a dish together to serve to a customer, the amount of food in the dish will be based on what is equal to 1 or 2 or 3 cp worth of food and service (cooking, cleaning, waiting on customers). A poor person spends 6 cp on food per day. Assuming three meals a day, 6 cp divided by three meals is 2 cp. This makes the math simple. If a tavern serves you some drink, they give you a minimum of 1 cp worth. 1 cup of ale is 4 cp, making ale a drink for a special occasion. The taverns probably water their ale down into grog unless you ask for ale to be served without being watered down.
Proposal 2. Hand wave all inconsequential expenses and don't worry about this minutia. It's easier, and players don't really care as long as it feels fair and plausible.
Proposal 3. Assume players have been throwing money around and making minor transactions all day, and just have the players deduce from their money the amount based on the lifestyle they choose to live by for each day they spend in a town or city, with a cap of Poor for a village. This is also fair and simple.
Proposal 4. Come up with your own fictional currency, like the shilling, farthing, doubloon, or whatever. Work out your own values for everything from the ground up. You can make something more intuitive and therefore easier to use, you won't have to track types of coins, you won't have to do any conversion, and it can give character to your setting, but it's probably effortful.
Recommendations
Proposals 2 and 3 together, or just eff it.
