I'd be curious what the game requirements are for the tactical shoot and why they would mandate a rail, if at all. That's the first I've heard of that; nothing wrong with the requirement just seems strange.
I got a tacti-old light I got with a Sig 226 that I picked up a couple years ago that you are welcome to for free if you really need and want it, you pay shipping. It fits underneath the dust cover and friction bolts onto the front trigger guard. The caveat is that you will definitely have to shim the thing before use as the 226 has a nice 1/8" screw divot in the triggerguard from the guy who first installed it and tightened it down. Am pretty sure the alloy frame of your Beretta would have the same fate if you didn't take precautions.
Note though as soon as you throw anything on that rail or that light up front, you have to ask yourself how are you going to holster it, if that is necessary. I can't see it being kosher forgoing a holster to just to have a light on the front. I'd have to agree with IM Lugger that crossed wrists and a flashlight might be the cheapest, easiest route for you in the end.
If you are set on getting a new pistol, I echo what everyone else said about if you are shooting factory: stick with the 9mm unless your tastes or your match requirements require something else. It'll be cheaper than .40 or .45, you can run one ammo in both pistols, and is lower recoiling which is better if 9mm works in this tactical game.