I wouldn't recommend trying to sneak anything illegal into the country. That's not a good idea. In a sense, MacG!ver is correct - to a point. The recomendation to sneak it over is foolish. You have to declare everything you bring over the border.
But you could technically part out an AEG and bring all the parts except the receiver or a silencer (if you have one). You can declare the parts and legally import them. Then you can get then get a new body for your gun once you're here and rebuild it. The bodies are still expensive here, but it's cheaper than buying a whole gun.