TTS used to have a pretty good pricetag, but it seem to be out of stock now. I only see the replacement bulb on sale there at this time:
TTS
The nice thing about HIDs is that their high blue spectra content will carry farther in water than incandescents, whose shorter wavelengths lose energy more quickly when submerged. The LC100 is not one light you'd "compare over the counter" (as their own marketing material states)
Frankly, I can't think of any light - waterproof or otherwise - that has the same brightness, runtime, weight, bulb-life and battery flexibility (you can use C-cells or a special rechargeable kit) and price as the LC100. And if you're diving to take pix or videos, this light will more than double up for that duty.