[dejv]

100 or even 200 will be quite a hard target to hit even considering BOM. Most bare bone optics setup will cost you maybe 100, 130 USD. Unless you find some spare parts or go DVD grating route. The best way is to search for ocean optics parts on eBay. There are multiple "benches", sensors and optics sets available most of the time. Still, it will be more than 200.