You could do what you're proposing with a single Hikvision camera (current favorite on the price-per-performance scale), a PIR sensor (I like Crow, or Optex), and some sort of internet connection (the email has to get from the cabin to you somehow).  

Most cabins are not particularly large, so a single camera in the common area might be enough.  You could put in several if you were so inclined, but you could start with one.  

I think you could get the hardware side of things done for a couple of hundred bucks.