You probably don't want "decent video quality", but here's three 640x480 wireless ip cams from $120-$200 (normal, night-vision & pan/tilt):http://www.monoprice.com/products/subde ... id=1101701
What you should be looking at is logitecs HD solution for $300:http://www.logitech.com/en-us/video-sec ... lder#page0
You'll need one "Master System" camera that plugs into power and network. Then each additional camera ($199-$299) just plug into power (Ethernet over Power networking - not wireless).
All of the solutions above have movement alerts (like sending you an email) and options to only record when movement is seen (logitecs lets you select where it will look). They also all have free iOS app, Android app & Web interfaces that can control multiple cameras.
Now for the legality of it. If no one is legally permitted in this particular location, then isn't it ok to leave a camera running there? Or would recording a trespasser actually be illegal?