Don't do it... you obviously don't know what type/style of pew you like, try as many aeg's as you can first or you'll be spending a fortune to only regret the purchase & we'll/I'll end up offering you 60-70% what you paid when it ends up in the classifieds.
If that's not the answer you want to hear go onto youtube and watch as many gbbr video's as you can.
If you do buy a GBBR, get a Calico, CZ Scorpion, L85A2 or a G3 etc coz I don't have one of these yet.