Here's a low cost option for multiple motion operated camera's.
http://www.ebay.com/itm/Smallest-Mini-HD...=item337142ed30
The micro SD cards are cheap, I have a key chain camera similar to this that I fly on some of my RC aircraft, it takes decent video but it doesn't have motion activation.

I just ordered this camera to set up at my cabin and operate when I'm not there, it should be easy to conceal and keep out of the weather, I'll let ya'll know how it works after a couple of weeks in the cold weather.