The Public Labs Website [1] offers plans and parts to build a simple spectrometer using easily obtainable items such as a webcam and a CD as a diffraction grater. While their primary goal is to use it to identify pollution, it can be used for any task which can make use of a low resolution spectrometer.
The plans are pretty straight forward and the device looks pretty easy to build. The biggest drawback is that it’s not exactly the sturdiest device. While the lack of a sturdy structure does lower the cost and make it easier to build, it does decrease it’s reliability.
I would be very interested if SparkFun would sell a sturdier, more reliable version of it. Perhaps pot the electronics to reduce shock and water damage. It’d be really cool if it could be a device that could be used in the field. The hardware is licensed under the CERN Open Hardware License [2] which if I’m reading it correctly, does allow Commercial use, provided, like the GPL, you give the customer the documentation and plans.
Just thought it’d be really damn cool to be able to buy a cheap and reliable spectrometer on SparkFun!