Right now, I don't know how legitimate it is and it is Amazon but there is this listing from one of Amazon's deal companies (an acquisition called woot):

https://www.amazon.com/dp/B08J1THV9G

$27 for 440 n95 aura masks.

Doubt this lasts, seems like a mistake or maybe there's something going on there. Probably don't have a distant expiration date. Also might want to consider the elastic on them may have been subjected to stresses from bad storage but even if they only last one wear they're so cheap you're still saving money. And you can always buy covered elastic and staple it yourself to the masks in place of the ones they come with. For this price it would be worth it I think.

So hypothetically this should probably be more reliable than the third party sellers on amazon. Probably surplus from somewhere, probably not brand new but hopefully still good.

I've had success buying them in bulk from resellers, whether you trust that or not is up to you but it's worked out well for us so far. Another good option is buying an elastomeric respirator, it's much cheaper in the long run and usually provide better protection. Downside is that they often have exhalation valves and thus don't provide source control (though most people aren't protecting themselves anyways so tbh it's kind of hard for me to care about them at this point) and, frankly, you'll probably be harassed wearing one. There's more low-key options like the envo but they tend to not fit great in my experience and are more expensive (though probably still less expensive than buying disposable respirators).

I've been getting 3M Aura 9205 from Home Depot at around $2.20/pc in boxes of 10. Expensive but I re-use them for a while, and fix them with a stapler if the rubber band snaps (that happens a lot). I've used various cheaper masks and not liked them as much.

Directly from the manufacturer in bulk or from bulk deals I see on social media. I can't mention the brands without having bad opsec sorry. I have my cost down to around $1 per mask and wear them for around 20-40 hours before using a new one (I go by appearance, the fibers start to get soft).

Mask blocs are great and do this kind of thing all the time. Get involved with your local one!

Aside from specific mask brands/websites, this is how I keep mask-wearing affordable (for me, I aim for <$2/mask overall)

-Shop sales/subscriptions -Buy in bulk when possible -utilize local mask blocs!! -started a group chat on signal where me and friends alert each other to sales or pool resources for group-buys -I re-wear my masks. Probably close to 25-30hrs each. I leave them to dry for a few days to a week in between depending on my stock and schedule and toss them when the straps wear out or they begin to look dirty/lose shape.

Ok for brands- I can't remember the N95 I usually wear, but that's my most expensive mask and I save that for longer term wear and higher risk like work. I'll try to remember to link but I always wait for the sale. Then Wellbefore and Bonafide (bonafide lowers price the more you buy, and usually has a 25% coupon code). Wellbefore is a little pricey but they have a subscription price thay helps.

government surplus sites

some will give them free or really dirt cheap