Not to sound like a smart ass

pay him what you think he is worth based on his experience, tasks performed, and what your company can handle.

When I worked at a radio station our interns made less than minimum wage but erned credit for their time and assisted with projects in the studio, went on remotes, etc. It was fun, meaningful, and earned them beer money.

The interns at the company I work at now make from minimum wage up to $25 a hour depending on what exactly they do. In any case, the pay delivered should be appropriate to the work being done. If he does a great job you can always offer incentives and bonuses after completion of projects. Some schools have rules about interns pay so check with them.