Use monk's cloth. You can get it at JoAnn Fabric for $9.99 per yard. Then get Dark Brown RIT Fabric Dye (also at JoAnn). Definately check out these two sites: The first one for the AMAZING mask tutorial:

And this one for the accessories:

For the boots, I got a pair of rubber rain boots from Wal Mart. I wrapped them in duck tape, making sure to wrinkle the tape as I put it on. Then I painted with 3 different shades of brown spray paint, then LIGHTLY went over the boots with black spraypaint. They look awesome! You can also get everything you need for the mask from RadioShack, JoAnn Fabric, and the LEDs for the lights, look on eBay first. If they dont have the Panther Vision ones suggested in the tutorial, check at Lowes. In all, my son's costume is coming out to around $350. Im going to put up a website soon with step by step instructions for everything. I'll post a link on here when its done. Im just waiting on the LEDs, Resin Blaster, Resin Droid Caller, Ammo Pouches to arrive.