One of the tasks for the coming release of OpenPatrician is a better representation of the price development of wares with respect to the amount that is available. The idea is to define the curve visually and then transform the parameters of the curve into a formula that allows the computation of the price of the ware, given an available amount.
A natural choice for that is to define the curve as a Bezière curve with is very intuitive to tweak until the curve looks the way you want.