The charge per mile for process servers varies, just like the fees do. With fees ranging from $20-$100 across the country, the mileage rates also vary, depending on where you are in the country. It probably also depends on the process server or company hired. For more information, go to http://www.ehow.com/info_7799884_average-cost-hire-process-server.html
Most process servers do charge for miles traveled to serve documents, but this is set from business to business. $0.55 per mile is a general benchmark in 2011, but it is up to the particular process server to decide on mileage charges on an individual basis.