My starting point is the Cree XR-E 1000 kit with the Q5 Bin option from Cutter Electronics. This will be powered by the cheapest 7.2v battery pack I could find.
I still don't know what I'm going to use for an enclosure/case, but I'm sure that won't be too difficult to figure out.
For reference, anyone who has seen my Fenix flashlight in action has only seen a 100-120 lumen light. This one should be about twice as bright. My only problem with the kit is that it has an 8 degree beam width. I'm thinking that might be too narrow for general use. I'll find out eventually.