As an Airsoft palyer for the last decade, I have played with a few light options. The cheapest route would be a simple SF G2 with a Malkoff M60. And a simple weaver mount 1" scope ring to mount the light to a tactical rail. Depending on your weapon and its furniture you might want to get a G&P or similar remote tail/tape switch.
I have a SF M952P Weaponlight on my P90.
http://www.candlepowerforums.com/vb/showpost.php?p=2691718&postcount=398
In the picture I mounted my Turbo Kroma head. Normally it has a SF M2 bezel.
Watch this video I made.
http://www.youtube.com/watch?v=oaT4IbPE6go
I use a Blackhawk gladius and the SF Weaponlight. The strobing light you see is the gladius and the bright light is the SF. If you read the info part of my video, it tells you that the BB shot out the lens of my SF light. Not to worry as SF replaced it for free.
What kind of game are you playing? Outdoors or indoor CQB?
There are different low light techniques when using a flashlight in a tactical situation. First lesson is "People shoot at the light" so you have to think carefully how you use the light. Watch my video, I onyl use the light to blind or disorient the opponent. but timing is crucial. You should unleash the bright light just before you open fire. There are other techniques, you should google "Surefire Low light techniques" very basic ideas but will give you an edge in airsoft.
For outdoor games flashlights are almost unecessary. ambient light from the moon or city lights is enough. plus you want to stay hidden in the dark. However if you are trying to identify a long threat, then you might want to consider getting a light with a lot of throw. I was playing a zombie game and my SF M6 with the MN21 500 lumen bulb made a HUGE impact on the game. the zombie opponents literally turned away from the bright light and I was able to illuminate large sections of open terrain to search for possible threats.
If you have any question pm me. here is an ASCII flashlight to get you started
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