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[Bricabrac]

I'm working on a game about being a travelling merchant, so the gameplay revolves around buying and selling stuff.
The problem is, I know shit about math. I even fleed away from Science High School when I was younger! I need a way to balance the price of everything, and I don't really know where to start.
Anyone has tutorials, useful tips or advices? I read a few articles about balancing the economy of an RPG, but they all boiled down to "it doesn't have to be realistic". Some general rules to keep in mind would surely simplify my work.

[readyplaygames]

I'm in the same boat. I had prices for everything that I literally just made up as I was creating the items. The only thing I could do was to constantly ask my beta testers if anything is too pricey or cheap, and change it accordingly.

[voidSkipper]

If the game is about being a merchant, you probably want some price fluctuation and differences in there or it's going to seem very strange.

There's not much point being a merchant if the potion made from the leaves of the enchanted elven forest costs the same in the dwarvern mines' tavern as it does in the forest general store.

Another thing to consider is general market cycles, where the price of things in general can fluctuate over time.

It's worth considering whether or not the player himself has any effect on the price of things - for example, you go to the spider kingdom and buy every bail of silk they have. The supply of silk nosedives world-wide with no change in demand, forcing prices up, which you can then scalp the buyers with when you bring the silk to where it's wanted.

So I guess the most important factors are:
-At game start, the player shouldn't be locked out of the market by steep prices or incredibly thin margins
-There should be a reason to buy, travel and sell
-If the player's actions do affect the global economy, it needs to be on a scale where the player has an impact, but not such an impact that they can single-handedly bring down the economy and make the game trivial.

[valambrian]

You can use tabletop RPG books as guidelines. Pick a setting that's close to yours and I'm sure you can Google more data that you'll know what to do with.

[HoffmanIV]

Price the materials that make up goods to some kind of standard (100/pound of wood, 200/pound of steel, etc.), multiply it by weight, a labor modifier (difficulty to make the good) and supply or demand modifier (how common the good is, how much other people want the good), and maybe factor in a tax.

So P (price of item) =  W (weight of materials) x C (cost of material) x L (labor modifier) x [D (demand) / S(supply)] x T (tax rate).

The numbers from there on are arbitrary, but be consistent in how you plot the variables.

[Magurp244]

Another method of figuring out an economy is through world building.

For example, an item is only worth what people are willing to pay, to a man dying of thirst a glass of water is worth anything and everything, where as an apple in a forest full of apple trees is worth nothing as people can pick it for themselves. Economies work by limiting supply, either naturally or artificially, to create demand (like picking all the apples and burning the forest). So when making an economy you should try thinking about what regions your merchant is travelling too, what kinds of people they deal with, and what sorts of things they make/grow. How would those compare to other regions/people? Are they hard to make/grow? Are people price gouging others because they control the only supply of a particular good? And so forth and so on, exact numbers are not quite as relevant as the motivations behind them.

[valrus]

Another way to think about pricing is in terms of regional price relationships.  If you have something made at point A and sold at point B, the difference in its price between B and A will be roughly proportional to how hard it is to get from B to A.  (That's because if it's underpriced for the length and difficulty of the run, merchants will make that run less, and supply will drop, and the price will rise, while if it's overpriced for the length and difficulty of the run, merchants will make that run more, supply will rise, and the price will drop.  But you don't have to simulate all that; you can just set prices accordingly.)

So you can have various "source points" on your map (conceptually, you don't have to show them) plus "destination points" (e.g., market towns).  Set a base price of each commodity, and then set its sale price in each market town according to its distance from the nearest source point for that commodity.  It depends on your historical era how much the price rises per mile, but for example in Roman times the price of a good was raised by about 40% per 100 miles it traveled over land.  So roughly:

  market_price = base_price * (1.00337 ^ miles_traveled)

Keep in mind that this rate of change will differ depending on whether you're traveling over rough terrain (slower), water (much faster), whether there are bandits, etc.  You might want to have a grid of values.  So say each square represents 10 square miles, and hills are 1.05, plains are 1.04, roads are 1.03, and water is 1.01.  The market price = the base price, multiplied by each square it travels through to get to market.

Beyond this you want prices to fluctuate, of course, or else it'd be pretty boring.  But this is a way to set the average price for each commodity at each market, around which the momentary prices can fluctuate.

[Bricabrac]

Price the materials that make up goods to some kind of standard (100/pound of wood, 200/pound of steel, etc.), multiply it by weight, a labor modifier (difficulty to make the good) and supply or demand modifier (how common the good is, how much other people want the good), and maybe factor in a tax.

So P (price of item) =  W (weight of materials) x C (cost of material) x L (labor modifier) x [D (demand) / S(supply)] x T (tax rate).

The numbers from there on are arbitrary, but be consistent in how you plot the variables.

THIS. This was exactly the kind of advice I needed. Thank you!
Many thanks to everybody else for the useful tips - I was already setting regional prices, it's nice to know it sounds like a good idea for you too.