How come if you try and buy a set of Bi-Xenon headlights for a C-Class they are a $770 option through the dealer, but if you buy them outright they are like $2300?

I really like the look of the new Bi Xenon lights and i would imagine a huge difference in nightime driving.. How can i get a pair of these for a reasonable price.. I like the idea of paying $770 for both of them!

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2001 Mercedes-Benz C320 3.2
1991 Mercedes-Benz 300E 3.0