orangeLearner:
So I have been wondering about wireless sensor networks and home automation for a while. I wanted to know how low I could really push down the price of bi-directional sensor network.
http://shop.moderndevice.com/products/jeenode-kit
The JeeNode (kit) at $18.90 in lots of 10 is a bit more expensive than you wanted but a lot less than $45.
That is all on one board, and uses 3.3V which means it will have low power consumption.