To create a plugin for exporting from Maya is no small task. PM Matt the Man as he created on for indigo.
I don't think a MEL script would cut it, you may need to use the Maya API, and that means C++ to create a mll file.
Have a search for GTA Mod Sites, they may already have one done, but I think its more than likely they exist for MAX, as that is the software used by Rockstar.
Chris (formerly R@nSiD)
When the power of love overcomes the love of power the world will truely know peace - Jimmy Hendrix
Winner SM VFX Challenge 1
3rd Place SM SteamPunk Challenge (May 2007)