LED Poi AG3/LR41/SR41

Tried and tested. :)

These were specifically designed to use three AG3 batteries - the cheapest batteries I can find on Ebay - and a single 5mm LED.

100 of these batteries is $4 shipped:
http://www.ebay.com/itm/Wholesale-100pcs-AG3-LR41-SR41-392-196-Alkaline-Button-Cell-Coin-Battery-/291376606158?pt=LH_DefaultDomain_0&hash=item43d7662bce

And 100 LEDs is $1.31 shipped:
http://www.ebay.com/itm/Lot-Of-100-Pcs-5mm-Round-Blue-LED-Super-Bright-Bulb-Panel-Board-Lamp-Light-/261752989837?pt=