I'd find useful a solution which shows UV and IR wavelengths too. The Everfine SPIC-200 with one sensor used for both spectrometer and light meter costs about $1K and the SFIM-300 with two sensors, one dedicated to the spectrometer and one for the light meter and costs about $2K. The more expensive is more accurate and includes use at low hertz when testing flickering. Both are industrial meters but the SPIC-200 should be good for cinematography.
The SFIM-300 is used by SLR Magic.
Andrew Chan and I discussed the Cine Meter product that John Brawley suggested with the Luxi attachment for the iPhone. Andrew cautioned that incident meters that use the traditional half-globe (that gathers light from a very wide angle) may not give measurements as useful as a meter like the Everfine meters that use a flat surface for incident readings. That half-globe approach was invented many decades ago and used ever since, but it doesn't mean it's the best approach. Luxi uses a half-globe, but a better solution would be to mount a wide angle lens with a flat piece of white semi-opaque plastic in front of the lens.
SFIM-300
http://www.everfine.net/productinfo.php?pid=188&fid=10SPIC-200
http://www.everfine.net/productinfo.php?pid=166&fid=10Sent from my iPad using Tapatalk