Electronics store= Active surplus. cheap cheap cheap, and fun to wander around.

I've got my old marwi nightpro light which kicked the bucket (not sure why) but it had a 15W 6V MR11 halogen. 35W 12V are a lot easier to come by for a lot less money and they fit the housing perfectly, so that takes care of the hardest part for me as I already have the housing, reflector and mounting.

Next up is power supply... and you can get 2.3Ah 12V batteries at Active surplus for $2 each. I bought four, and I'll hook them up in parallel depending how much burn time I want. The only problem is that they're very heavy- each one is 2lbs. For my commuter bike weight is kind of a moot point anyhow.

I do have a 35W HID bulb, ballast and starter... but I'm not sure how I'd get it mounted to a reflector/mount. It's a standard H7 bulb, but I don't know anything besides a car headlight which would fit that and that's a bit much to mount on the bars!