I took the time to sort out the total cost per sensor. These are all US parts from Adafruit or SparkFun except for the radios which I bought through the MySensors Ebay link. (It'd be interesting to compare the total cost with all China direct parts.)
Arduino Pro Mini 328 - 3.3V/8MHz $9.95
Half Sized Permaproto Board $4.16
Battery Holder $1.95
Spring Terminal Blocks $0.99
3 AA NiMH $8.05
RHT03 Temp/Humidity $8.96
TSL2561 Luminosity $5.95
- Wire, Solder and two resistors.
I'm also excited to see the battery life. I'm hoping it will be good. Each sensor has a voltage divider on A3 thats measuring the voltage from the batteries.
@Anticimex I'm hoping these are as good of an option because I can configure them in different ways depending on what sensors I have on the node. I'm planning on building some with motion sensing, door/window open/close, uv, barometric pressure and 3d axis. The top part of the sensor would be identical.
@Damme Here is the same picture served statically rather than from OwnCloud: