# Formula: the higher A is, the lower B gets

I'm developing a game where I've come to the point where I need a formula to calculate the gold cost of a resource. I want the gold to get lower the more resources are sold, so if A is gold and B is the resource, the higher B gets, the lower A needs to be. I'm posting this here because I'm looking for some different options and the math board seems like a logical place to ask for help with a formula.

One of the simplest formulas would be $A=\frac{c}{B^{n}}$ where $c$ and $n$ are arbitrary constants. As $n$ increases, the magnitude of the rate at which $A$ decreases with increasing $B$ increases. $c$ works similarly, but not identically. You can experiment and plug in values to decide what is best.