Get a kevlar imatation vest, which you could probably get from most SWAT officer vests. Just tamper with that a bit until it's all black, and then create the skull stencil out of card paper. Apply some light paint, and you're good. Although, the neck guard might be a bit harder. Try getting a black hockey neck guard, maybe a goalie one. They're usually only 8-10 bucks, and you could stitch it to the vest.
Of course, you might need to stictch on some clip packs and whatnot, if you want it very accurate.