Drive over to the states, do some shopping, hide a jg or echo and some upgrade parts in your trunk. Ditch the box. When you get back, have someone upgrade it for you and work on getting a metal body.
For $300 you can have a very nicely upgraded gun. New. Some even have metal bodies.
Then instead of buying a gbb(pain in the ass) get the pistol version of the m4. That way all your guns use the same mags. Saves more and aegs are more reliable and as sidearms are awesome. Just my opinion.
Grand Poobah of T.W.A.T.