https://www.quora.com/What-is-a-good-affordable-gas-mask-that-can-filter-bio-hazards-like-viruses-and-germs
The good news is that a military - civilian. gas / particle / biohazard mask like this may be sourced new for under $15.00 USD, and the filters can be expected to last for up to one week of isolation use before replacing with new filters.
The Bad news is that it will probably be shipped by mail from China, and might soon be back ordered.
Another site with ratings
https://bestsurvival.org/best-gas-mask/
as this one made in America, I believe
PD-100 Full Face Respirator/ N95 Equivalent Filter Set
https://parcildistribution.com/products/pd100-full-face-respirator