How much does a video surveillance system cost for ADT or Brinks?

I currently have a basic security system with ADT. I am looking into getting video surveillance added on. Does anybody have this video surveillance package? If so, can you give me a short breakdown of how it works and I definitely am curious on the pricing of it. I just wanted to get a camera in back and in front of my place, nothing inside. A few years back, I ran with some very bad company. I have had empty threats made upon me and I am just worried. The basic system isn't something that makes me feel very safe. I already am in the process of getting my foid card and such...I really want information on video security costs. ADT doesn't place prices on their site...I would even be up to switching security providers if another company has a better security system. I appreciate your help in advance. Thanks!