If you are willing to go another step beyond the paper products you could buy sheets of syntra at a sign shop for $25 a sheet and put the printed out templates from the pep program on there. You could do it with a straigh edge and a utility knife. Take VERY special care for all the cutting that you will have to do. You can score the syntra, which is to say you can make a light pass once, then another, and by the third you can dig in a little deeper. Syntra can be scored twice then snapped on straight lines. Curves will have to be cut through. It will take some work but it makes good armor. Use CA glue, medium thickness, to put the pieces together. CA is cyranoacrylate and it is in any hobby shop, also get the accelerator spray to help hurry the process. BE EXTREMELY CAREFUL as this is super glue with attitude. Have parents help and supervise! But I think it can be done this way. It will take more time than cutting cardstock but it will be tougher. You can spray the armor down with spray on bed liner that comes in a can to give it texture and strength.
That may work. I built a Boba Fett and a Colonial Marine that way and have used those same techniques in modifying my star Wars armor.
Just remember, this is a suggestion or an idea for you so results may vary. You have precious little time until Halloween.