Paying $130 for a 3W LED system is really overkill. 3-watt Luxeon Stars cost less than $20 and have a Vf of like 3,4 volt (white). Can definitely be driven by 6V, even 4.5. Driving them is really easy, if you don't care about nuking away some power as heat. Just do a LED series resistor calculation like you would do with any other LED, but keep resistor heat margins and LED current margins generously large.
Want to be more effective? There's always buck-dump inductive drivers but it requires knowledge, some effort and a microcontroller.
http://www.microchip.com/stellent/id...pnote=en012124
if you need more help just let me know. I'm studying EE and pretty interested in LED applications