Huper Optik ceramic is around $400 or more... was quoted $550 from a reputable guy around NYC.

I went with a carbon which was $220 for all but the windshield as well. 35% all around.

50% may not do much - may as well not bother. When you say front I assume you mean the front sides. 35% is dark enough to look good (with the white) but light enough that cops can still see you on a bright day. My front sides are "illegal" too but haven't had any trouble.

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'08 X5 3.0si - Alpine White / Saddle Brown interior
Specs: Sport Pkg, Premium Pkg, Tech Pkg, Comfort Access, Aero Kit, Style 433 staggered 20s on Conti DWS
Mods: Carbon 35 tint, LED angel eyes, GP Thunder 7500k fogs, H&R 20mm/25mm spacers, clear reflectors, gunsmoke-tinted taillights
Coded: Digital speedo, windows/sunroof/tailgate close via keyfob

X5 pics at Flickr