I got a SF 6P with a 400lm chinese dropin on my 22lr AR. The upper has a Troy rail with an Arson Machine Co. direct mount for the light. Works good to keep things away from my chickens. Since its a 22lr any light will probably work. But I would do a SF G2X Tactical in whatever mount that will work with what is on the front of your gun. You can pick up the light for around $50 from various online places. Then mounts start around $20 for OK ones, and go up from there. There is no reason you couldn't get a light and mount for well under $100. But I would second getting a decent little pistol for HD stuff. I much prefer pistols indoors. Just easier to handle. But thats just me. Also, if you want something for HD, you can get a cheap used shotgun for not a lot of dough. I have scored a few over the years for around $100 or so. Most have been pumps some have been break open single shots. But they go boom and pack a bit more punch than the 22lr. Heck you can get a Maverick 88 usually for under or around $200. Put a magpul forend for the mossberg 500 on it (assuming it will fit) and you can add a light pretty easily to that. Could probably do the whole thing for around $250-300 and it would be way more better than a 22. Food for thought. To each his own.