Having just put a new camera system on my house, i can recommend the Sannce 4 camera 1tb memory system at 119 pounds. Anyone can fit one as it is just plug in parts all supplied in the package. 1080 HD quality with zoom in and will store about 12 days with a 1tb hard drive built in.
You will need a screen or smart TV or iphone to view. I bought a 21 inch monitor for 85 pounds.
Fitted it in the 2nd floor spare bedroom which is kept shut up. You do need to keep the recorder out of the reach of anyone entering the house.
Very pleased with this system.