Immedia Semiconductor via Amazon offers Prime members the Blink XT Home Security Camera System for $79.99 with free shipping. (Best Buy charges the same.) That's the lowest price we could find by $50, although we saw it for a buck less in December. The system includes one camera with built-in motion sensor and the sync module. It's compatible with iOS or Android devices.

Note: you can also buy the 2-camera system for $139.99.