Military surplus M51 are the only protective masks that are rated for ballistics and chemical protection. They are explicitly designed for people fighting in a chemical attack, and remain attached-as-fuck to their face with a good seal, industrial ones are not. There is a reason why they are so expensive to an exclusionary price.
The industrial ones are simply N95 filters with shitty seals and aren't rated to protect against chemical attacks such as CS gas.
I promise you, from personal experience, do not fuck around with CS gas, or think a cheap mask will protect you. That shit is a powerful irritant and does a good fucking job of it.
Either you go cheap and get stomped anyways or go prepared and return home safe. Your choice.