How much cost a graduate student to a supervisor?
As stated in the comments, this is impossible to give a general answer to; you would need to choose a field and a country. 

That said, I think the factors you list are generally pretty negligible. The major expenses are usually the stipend, tuition, and overhead on the stipend+tuition. That can easily be $60K USD per student per year, often more. Also, students require considerable training (i.e., faculty time) before they start becoming useful. Those are the main drawbacks of hiring a student; no one is too concerned about the extra pens or an occasional conference fee.