mike wrote:
I was thinking it should be easy to find some $40 fan/pump that would
deliver low-pressure air from a clean air location, via hose, to a
mask.

Not so. They all seem to want many hundreds of dollars.

What gives? I'm not asking suck air through a garden hose, but this
doesn't seem like a big feat of engineering. I don't even need HEPA
filters.

When I was a lad, the shop teacher made a diving helmet out of a 5-gallon
bucket, a sealed plexiglass window, and an air hose. He strapped window
weights to it and we boys took turns using it to scrub the pool walls.
Worked swell.