Supply and Demand of Soccer Players

I am trying to create supply and demand functions of soccer players. So far I have D(P, m, ) and S(P, n, ). So P is price, as price increases, D decreases and S increases. m stands for finances of the club, so as m increases, D increases. n stands for number of players, as the number of players increases, the supply of players increases. I was wondering if anyone had any thoughts on two variables that could negatively effect supply and demand. So as x goes up, supply/demand goes down. I have tried to think of ones like team rep, where as team rep goes down, D goes up (I have looked up previous records of teams and transfers and found this to vary and not a good measurement). Any thoughts?