[joshvm]

Have a look at the work by Christian Buil [0]. He's been building incredible DIY astronomy widgets for years.

Off the shelf you're looking at around $8k for a spectrometer from Ocean Optics. Just point the fibre at sun on a white PTFE plate outside (teflon has pretty uniform reflectivity) and it should work. You generally need an InGaAs sensor to go beyond 1000 nm with any appreciable sensitivity. Silicon is still sensitive to around 1200, but performance drops significantly. The solar image from NASA is only in the visible anyway, but as I mentioned in another post the simplest way to do this is to use a high lines per mm grating (e.g. 1200) and rotate it so you capture multiple spectra in shorter ranges.

[0] http://www.astrosurf.com/buil/spectrographs.html

[1] https://www.oceaninsight.com/products/spectrometers/general-...