Hamamatsu (Japanese optical engineering company) is offering micro-spectrometer heads, which are quite affordable (at least those for VIS spectrum) and easy to work with and they are much more precise than other DIY solutions.
Are there competitors/shanzhaied versions out yet? A cursory google search of MEMS nir specs turns up a few hits.
Not shanzhaied, but another alternative spectrum sensor for VIS/NIR(390nm - 1000nm) is nanolambda NSP32. www.nanolambda.net
I checked datasheet and resolution is something like 25nm, not that great for most common application. Those Hamamatsu micro-heads are about 14nm (which is still not good), commercial benchtop instruments around 4nm.
There is even Si-Ware FTIR MEMS sensor. It is quite pricey (more then 1K USD) and resolution is not that great, but pricey will drop eventually and it might be good enough for some applications.