Webcams offer a low-budget alternative worth exploring.
Webcams are small, usually round, video cameras that send images to your computer. From there they're transmitted to other computers over an internet connection - in real time. Just a computer, a webcam with accompanying software, and some kind of phone connection. The most common maximum configurations for a webcam are 640x480 resolution and 30 frames per second in frame speed. If you could actually achieve these maximums, you would have a clear 4x6 or larger image with movie-quality frame speed.