But people don't for some reason. And I'm not sure what you're getting at with a cheap "agent" you can get for $50 that would be effective when you factor in practical issues like delivery. Bleach plus ammonia will produces chlorine gas which is lethal. Might work in a confined space without ventilation, where people can't move (like maybe a crowded train). This happened in Japan with the sarin gas attacks. But if you read the background on those, there was considerable time and expense in producing the agent, and it hasn't been repeated since.