First, it will depend on what state you live. In many states, there is a cap on how much a dealership can charge you on the document fee when buying a car. Follow the link for the chart. In states where the doc fee isn't regulated and is anything over $100, simply cross it off and tell him you aren't paying an excessive document fee.
I paid $45 for the doc fee in California, the limit on what the dealer can charge.
Good luck and don't be afraid to show him the link on what fees can and cannot be charged if you are in a state where this is regulated.