While I agree we should find a substitute, I think huffing purifier fumes are going to kill you faster than the spores. You'll be basically huffing bronze and getting a lethal dose.
Just so this is constructive, I believe we should just be able to craft makeshift filters with less quality/durability by burning wooden bits and using wood charcoal as a substitute. Of course, filters use activated charcoal, but for the sake of having an alternative, It wouldn't hurt.
Pros:
Cheaper to make as long as you have an open flame or access to a furnace.
Doesn't filter the spores as well as a normal filter, but you'll still be able to make short runs across the sewer.
Cons:
Less durability, less quality, and runs out quicker.
You wouldn't want to use it unless you're broke, something you'll need to upgrade if you want to be efficient.