And yes, they can be quite expensive. Usually running up a bill into the hundreds to the thousands depending on how long it takes them to find out the person you've been wanting to track down.
And thankfully now you can easily perform a people search to find anyone online. All it takes is some simple information on your part such as the persons first or last name, or even an address or number, and you'll be able to find out exactly where the person lives at, their background history such as previous jobs, age, criminal records and a list of relatives
To get started with the most simple way to find a person nowadays, go here