Main character from a Shooter
Nintendo characters are much beloved by pop culture, but excellent marketing campaigns on Halo and Gears of War have at least introduced images of Master Chief and Marcus Fenix to the public. So you could get away with going as one of them for Halloween. But you’ll have a hard time doing it on the cheap.
Option 1: Marcus Fenix
Cost: $35 to $60 for the mask depending on retailer and however much money you want to spend on spray-painting cardboard boxes gray to pass for armor
Good luck breathing in that thing. Option 2: Homemade military
Cost: Cheap -- maybe even $30 cheap
You can find fatigues on the cheap at any army surplus store, and sometimes pick up vintage officer's coats from thrift shops. The trick with military costumes is knowing which military shooter game you're going for. Modern Warfare is easier to emphasize with desert camo and night vision goggles (real or replica), while Medal of Honor follows specific historical periods you’ll have to research in order to nail the look. If you want to get cute, get a ski mask and spray paint a skull on it, a la Modern Warfare 2's Ghost. Option 3: Master Chief
Cost: $30 to $800
Halo's Master Chief is just popular enough to have an officially licensed packaged costume for sale at most major retailers (includes half-helmet, printed jumpsuit with EVA molded chest piece, and gauntlets – and it comes in kids sizes, too). The truly hardcore, however, will want the pricey cosplay sets made of thick plastic armor plating and quilted jumpsuits. And you can forget sipping Halloween cocktails in that getup.