$700 and you'll need to designate a computer to be your DVR and server. And as long as you have an internet connection and Internet Explorer(Active X control) you can monitor it from anywhere in the world(or outer space if they have internet there). In addition to my computer(DVR), I have a little netbook hooked up to our TV in the bedroom, so that if I want to see what's happening outside, I just need to change inputs on the TV and take a peek.
A lot of people that come to the house for whatever don't even notice them and if they do they just shrug it off. I installed these when the house was being built so it made it easier, but if you can somehow fish the wires(one wire per camera-supplies power and carries the video signal) then it shouldn't be too bad to install on an existing home.
http://www.sunsecurity.com/security-cam ... ty-systems" onclick="window.open(this.href);return false;
BTW..I have no affiliation with the company.
-Cain