Either that or what I wanted to do with one currency (say coins) that were earned by clicking pets, and a second (gems) which would be earned a different way (i was thinking donations).
what i actually mean is: lets say a user buys a certain pet, which has been bought 1 time that day/week/month, resulting in it's price goin slightly up for everyone (just like in real life, when people are massively buying a product, then the price goes up) and when it hasn't been bought for a while, the price goes down (where you can specify the maximum increase and decrease values in percent in the admincp.