For the vests, use a brown paper bag and cut it out like this.  For swords, use the paint stir sticks (smooth, no points) if you have some or go to a paint store and see if they'll donate some to your cause.  For shields, use what are called "pizza rounds" which are 12-inch round pieces of corrugated cardboard which you can get really cheap from a packing supply store.  Then punch two holes in each shield and run a pipe cleaner through them for a handle. 

* If it's helpful, click here for a website that gives you a pattern for 1 and 3 piece armor.  It is intended as a Halloween costume, but that's okay! : )