Keep in mind you are purchasing the time of a professional not necessarily a solution. Often the answer you seek is elusive and will take some time to dig through records, analyze documents, find a new course to follow, etc. Any of which could still lead to a dead end. You have bought the time of the researcher, ideally with a lot of expertise in the area of your interest, who would be more effective or efficient than you. You may end of learning that there is no "Answer" to be had or that more time is needed and therefore, more money will have to be spent.
Heed Anne's advice for the best chance at an answer.