Supply, demand and price

I hope game design questions are acceptable here. If not, I’m sorry.

I’m developing a game in which players try to acquire commodities and sell them across territories to make money. Each territory has a certain demand for each commodity. The demand is increasing over time and decreasing when sales take place (filling the demand).

One of the aspects the player has to decide is the price of the commodity when selling. The price and the demand should affect the speed at which the player can sell, forcing the player to make a decision between selling fast for less profit or maximizing profit per unit but at a slower pace.

The problem I’m running into is how to determine at what speed the player can sell at what price. One solution I have come up to is determining a maximum price per commodity at which nothing will be sold and simply drawing a line/curve down to a price of 0 at which the player will sell at infinite speed. But a maximum price feels like cheating. Has anyone come up with a better solution or are there any examples? I know that games like Capitalism and Patrician work with a system like this.

This isn’t a game design question - it’s an economics question. I suggest you read up about supply and demand curves, or enrol on a basic economics class such as: