I believe the best light for the money right now is the Streamlight TLR-1 which can be found for $90ish. I have one mounted on my duty Glock 17 and it has been exceptional compared to my old Insight/Streamlight M3.
This light may be a bit too big for the 4013 though so you may want to look at the Streamlight TLR-3 which I believe is in the $70 range but I have no personal experience with it.
I hope this at least gives you some ideas anyway,
Scott