Andrew wrote an answer about Petzl Ultra Headlamp on December 9, 2010
Lithium Ion rechargeable battery, those are NOT cheap in any respect (try pricing out Li-Ion radio control car batteries, laptop batteries, etc)
IP66 rating. Takes a BEATING and smiles about it.
350 Lumens. Nothing is as bright, and it is not easy to make anything that bright, especially something that small, considering a 1 watt LED bulb produces 80-100 lumens and costs a decent sum.
3 year guarantee, INCLUDING the expensive battery.
Remote battery pack, for extreme cold and weight distribution.
You wanted to know why it was so expensive, you simply aren't going to find those features in a sub-$300 light, let alone one with Petzl's professional series reputation backing it up. To ErkMD, you won't see one out by years end, or in the next year, that you described, this is a very niche product. And, if your underwater with it, you don't want that brightness, it will highlight every speck of floating dust and it will be like putting on high beams in fog (unless you are in a swimming pool, in which case, why are you wearing a $400 headlamp...)