The Streamlight PolyTac LED is becoming a popular budget weapon light for use on a carbine. Streamlight has recently introduced a new version which may be even better suited to carbine use – the PolyTac LED HP.
It shares several features with the regular PolyTac LED like a “clickie” tailcap, IPX7 waterproof rating, 3 hours runtime (to 10% output), and durable polymer construction. However, the HP model increases the brightness to 150 lumens (versus 130 on the regular model) and features a wider, deeper reflector. Wider, deeper reflectors capture more of the light from the LED emitter and focus it into a tighter beam which results in a beam with a tight hot spot, more throw, and useful side spill. In other words, it should be a heck of a weapon light.
I have seen them for as little as $40 (give or take a few dollars). You could mount one in the excellent VTAC Light Mount and have a high quality weapon light for $60-70!