The good ones I've seen run for $150 - 200 a piece.

The cheap ones only send still images and don't work well in the dark.
There's a good one by D-Link, runs about $180, has it's own web server
built in, makes remote access very easy. The other site to look at is
www.smarthome.com. I've been told they are a bit overpriced, but it's a
good place to start.