O.k, so it is obvious that the CD/DVD idea should be scrapped for astro work..........bummer!
There are plenty of cheap 500l, 1,000l replica plastic gratings available on Ebay...................are these usesless also?
''Proper reflective diffraction gratings'' are very costly for larger sizes through Edmunds and other sources.
I guess that a 60 degree prism may be the next try............but where to get?