Reddit mentions of Giro Venti Bike Helmet, White

If you know of a store with some kind of clearance junk isle (wal mart, target, k mart, etc), dig around in it. You may be surprised what you find. I found these for $2. Blinking they should get around 150 hours battery time, if I recall. I put the red one on the back of my helmet and put the white one away for when I find another place to put it. Then I bought two more lights in a pack, a head and a tail, for $12. None too powerful, but tail lights don't need to be, and in my neighborhood I'm never too far away from a street light unless I really try.

If you have the right kind of helmet, you may find a literal headlight pretty easy to macguyver out of an otherwise cheap light not made for mounting. I've done this. In september (?) I got this pack of 3 headlamps for only $8+tax at a store. They're more than bright enough, and the adjustability is fabulous. Using just two zip ties I managed to fasten one securely to my giro venti. I love using it, all the reflective stuff for 40 yards in front of my lights up clear as day. Stop signs, license plates, reflectors, lane paint, glass and sand on the ground. If I set it to blink it actually looks like the stop signs and license plates are self-lit and blinking. And at such a cheap price I'm not too worried if something happens and I break/lose it.

So there you have it. $22+tax and I got seven lights, 4 in service at any time.

pro-tip: since it's april, april shower time, you should think about water-proofing your lights using pieces of spare inner tube. It holds nice and tight on all my lights' seams, and is easily dealt with when time to change batteries.