Well actually if you can get your hands on one the all black ICS guns are actually great.
Other than that there are plenty of guns in the AV classifieds section. If you're not picky about brand or anything you can find guns from $300 all the way to $3000+ depending on whats included and whats in the package, what kind of modifications were put into the gun, and how much use it's seen. $550 should get you a decent used package with gun, a couple mags, and a scope however I'm not sure of the market right now as I haven't been in the classifieds in a while to see what kind of packages are available right now (not in the market for another gun currently).
Note that airsoft batteries are basically just RC batteries just different shapes, they're both rated for high current output and such. You won't have any problem with customs regarding them. Certain pieces of gear however are a no-no (equipment that falls under ITAR, and other prohibited goods/parts like Receivers).
I bought my M4 for $450 used. It was just a basic package. Gun, battery, and scope. No mags, no charger, nothing extra. Eventually I'll buy more and more gear but start off with the basic fighting equipment and you can work your way up from there.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE