First you should define what type of private investigator you are needing or at least what you are needing them for, because not each private investigator may do work in the same field. Some may do process serving, skip tracing, surveillance, criminal and civil. These are just some of the fields, and there are many more. Each one is different in his\or prices. Some charge by the hour and some daily. The best way is to simply give a private investigators in your area a call and ask them for an estimate regarding your specific case.