I build a few, I use one with a 18350 body as my edc.
Triple Luminus SST-20 (3500k) 7$ include optics http://kaidomain.com/Flashlight-DIY-and-Tools/LED-Emitters-or-LED-Star-on-PCB/Triple-LED-On-PCB/Triple-SST-20-LED-Emitter-with-20mm-x-1_5mm-Copper-PCB-Parallel-w-optics
Two copper base plates a 16 and 20mm ($1,24 from Fasttech) Instead of the 20mm base plate you could also use a second glass lens.
Nanjg AK-47A driver $1.93 from Fasttech.
I desolder one 7135 regulator and put a FET on it. (comfychair-inspired quick+cheap+lazy single-sided 17DD FET-driver (poor man's nanjg92)) (The FET that I uses are from a old pc mainbord. )
Flash the driver with blf-a6 firmware.