How much does it cost to hire a private investigator? It depends on the PI company. Still Watch Investigations handles mostly infidelity and custody cases. Not every client can come up with a $5000 retainer. At Still Watch Investigations we will recommend the correct number of investigators for the job which can get expensive. Downtown Nashville nightlife investigations requires three investigators so a client can expect to pay up to $1000 for 4 hours of work. Some of our cases last for several months so we keep our rates very competitive. Our goal is to do the job right as cost effectively as we can for the client. There are many great investigators in the Nashville Tennessee area. A client should choose an investigator based on the investigator’s experience and ability to communicate with the client, not the rate.