The Romisen RC-M4 3V~8V Cree 1-Mode Flashlight looks pretty good especially for the price. Do you know if it has a bezel diameter to take the 1.25 inch 31.74 mm FM35 Surefire Red Filter attachment? The Ultrafire WF-501B seems to have the correct bezel diameter.

http://www.surefire.com/maxexp/main/co_disp/displ/prrfnbr/870/sesent/00/FM35-Red-Filter