Using a milling machine with a 4, 6, 16, 24 and a 26,5 mm mill this design is a possibility.
It is made from two pieces of aluminium each 60 by 35 mm, two P60 drop-ins from Kaidomain, lenses and o-rings from Dealextreme and a 12 mm switch. The XM-L LEDs on 20 mm stars are mounted directly on the finned rear section, thus giving the best heat transfer possible. The main body could be finned also.
Below is an animated assembly.
The drop-ins are $9,21 a piece including LED and LDO regulator. The lenses and o-rings are less than $1. Get your hands on some scrap aluminium, and you’re looking at a pretty cheap 1800 lumen lamp. For added power – just scale this thing to have more drop-ins….