Depends on what look you want to go for. Besides, you can always go as a Greenshirt. A Greenshirt is a guy in a mostly standard Army battledress uniform, which you can assemble at any military surplus store.

Once upon a time, I had hopes of anime cosplay as the titular character of Armor Hunter Mellowlink, which is sort of in the same vein. What the costume would have entailed for me:

Poncho
Camo-pattern hunting trousers (which you can get at WalMart for cheap)
Suspender type torso harness (look in hardware stores)
Heavy-duty tank-top shirt
Combat boots (I had work boots that were close enough)
Pony tail hairdo
War paint
Gloves
Fake guns (I actually own the official G.I.Joe Laser Tag(TM) pistol set...and my plan was to augment this with a bazooka assembled from a mailing tube and a defunct hairdryer unit)

I gave up on cosplay after a particularly pathetic Char Aznable I did. Got dead last in the Masquerade but won Char's Counterattack on VHS afterward, so I felt vindicated but also justified in quitting.

There's no shortage of websites devoted to Joe, including some that have pictures of the action figures and the package art.