Sadly, there is no direct answer to this question because results are strongly linked to what is known beforehand and what information can be found. There are too many variables to give even a close cost estimate.
A certain base amount of information is required to search for an individual or family. That individual or family needs to have been prolific at leaving historical records. The more migratory a person was, who did not leave many records of his presence in any one location, will significantly affected the ability to trace his or her later whereabouts and the time involved to do that.
Further, if one wants production on charts, graphs and a manuscript produced those costs increase from there if a researcher is looking for more than just the raw research findings. Once you have some idea of what you want to accomplish, contact us and we can maybe provide you with a better ballpark figure.