I've talked about AR500 armor before, and for those of you not familiar, it is basically a steel plate coated in a specialized PAXCON line-x, and will fit in all your cool guy armor carriers. It is heavy but it is significantly more affordable than other plates. It is also pretty tough. Demolition Ranch took these plates to task with 50 slugs. Feel free to fast forward a few minutes, and then skip ahead through the vid if you want (it can get a bit repetitive):
So the good news is that that none of the slugs penetrated the steel. That is pretty damned impressive, and all the steel had show for it was some bends and dents. The bad news is that the coating fell off pretty quickly. What the coating does is help against fragmentation and spall, which is what incoming rounds do against metal armor (you could see all the lead on the ground in the vid). The armor could stop a round from penetrating your chest, but if it showers your face and neck with lead chunks in is useless. I was surprised to see that coating split so quick, but I suppose if it were in that overly tactical armor carrier you picked up at the gun show, you'd probably be okay.
All that to be said, AR500 is still a solid value with level III plates starting at $60. Visit AR500 for more info.