As Doc said, getting AVed will give you access to so many more options. If you can't (or as some people, won't) then there's nothing anyone can do to stop you, but if you're really looking to get into airsoft in this country it is absolutely the best choice. You will be amazed by some of the things that become available to you in the AV sections and classifieds, and will wonder why you considered Buyairsoft (I presume) in the first place. Five hundred bucks can get you a lot more here than it can anywhere else.
Also did a quick search, and there looks to be a couple of M203s listed currently.
If you're set on the G&G, or against AVing, then that's your prerogative. Like the others I have no experience with that model or the MAX series in general, but it should do its job. Just make sure to switch out for the M100 spring that it comes with; that's a lot of velocity out of the box, and I really wouldn't recommend it for a starting player. You don't want to hurt someone or, for that matter as L473ncy said, your gun's internals.