or you could ignore the run of the mill guns and try to cobble together a support version g36? it'd be my choice and the lovely thing is if you manage to get a cheap clone its likely to be fireing at support weapon speeds already all you need is a long barrel and hand grip to turn a g36c into a k and a drum mag sorted.
personaly I dislike the american style airsoft guns almost as much as I do the guns themselves.
THB i dont think his budget would alow him to start going into gearbox work.... The ROF that most AEG kick out of standered is enough to keep anyones heads down