Dboys AEGs are well known for their affordability and high quality externals.  They produce great M4 and AK style airsoft guns in a variety of different setups.  Most of the models they produce come with a full metal body at amazingly low prices.  They usually feature a full metal gearbox as well.  If you're looking for a quality airsoft gun that doesn't break the bank Dboys is definitely worth a look.