Is money taken for photocopying papers considered unlawful, especially since the photocopying was done through personal effort and at a cost exceeding the original price?

It is not permissible to take an increase over the actual cost of photography, and the effort of work does not compensate you for it except with the students' consent. You are required to return what you have taken from them, even by indirect means, because the Prophet, peace and blessings be upon him, said: "The hand is responsible for what it takes until it returns it."