Dolby 3-D cinema uses narrow band color filters to achieve the stereoscopic effect.

Other systems use polarized light or use active shutter glasses to create the stereo effect. Dolby uses color filtering.

Dolby's 3-D cinema technology was actually licensed from a company called Infitech.

I don't know about cheap but the website is: http://www.infitec.net/index.php/en/

Or better: http://en.wikipedia.org/wiki/Infitec