Bungie has posted an article explaining all the detailed planning that went into the production of the $130 Legendary edition of Halo 3. Planning for the Legendary edition has been underway since June of 2005, when discussions were first held concerning what sort of molding method to use to form the helmet. In the end Microsoft chose injection molding and gave the project to one of its largest keyboard manufacturers in China. That's right, your fancy schmancy helmet is coming from a keyboard factory. According to the article, once peak capacity is reached at the factory, a new helmet will be produced every 12 seconds! Most of the article centers on the planning of the Legendary edition, but there are several photos of the manufacturing process sprinkled throughout as well.
Die-hard Halo fanatics may hit the "read" link to read the full article.