but 5x arctic cooling PC fans is ~$100. the commercial versions are easily available, more effective, no more expensive, and don't look like a box of furnace filters taped together.
But I'd honestly pay a premium for a commercial air purifier that just has a bunch of 120mm/140mm fan mounts instead of their "maybe tolerable at Very Low" integrated box-fan equivalent.
In general, all I've learned from online reviews of "quiet" appliances is that different people have very different definitions / criteria for "quiet".
i also have iqair which according to reviews is quiet at low speed. in my experience this quiet sounds like airplane (i got it replaced once. apparently it's just the way it is).
Sure, you can't hear it from 10ft away - but how much air is it moving at that setting?
I have various configurations of these PC fan setups and the Arctic P14 Pro that you can get 5 for $32 on amazon are honestly wildly effective and designed for applications with some static pressure (radiators and such).
So we're back to; effective or quiet, you're only going to get both with the PC fans, for now.
Rabbit Air (i think they closely related to conway) you can hang on the wall as art piece.