Is it permissible to take the price of photocopying the handouts only, or is it permissible to add a small amount for the effort expended in preparing them?

If the contract is for teaching only, without the preparation of handouts, it is permissible to ask for a price for them and sell them by mutual consent. However, if the contract includes the preparation of handouts as a condition or by custom, then it is not permissible to take compensation for them, because Muslims are bound by their conditions, and contracts must be fulfilled.