> Lab Safety Supply has them for $200-300 for face masks and $600 to well
> over $1000 for the air pumps. I wonder if you could just buy the mask and
> use a 2-stage regulator on your regular air compressor.

Used to work for an industrial pneumatic equipment company that set up heavy air compressors for this. You need an additional filter to capture the oil that comes from the compressor. Oil mist does very bad things to your lungs, namely suffocating you. The additional filter costs hundreds of dollars for the small ones, thousands for the large ones. It's pretty cost prohibitive.

If you want to rig up a system cheaply, there are two reasonable ways to go about it.

The real cheap way is to use a garden hose and suck on it. Breath in through the hose, and out through your nose. All by itself, this method is rather silly. But you can incorporate a scuba mouthpiece to make the breathing easier.

The other way is to us a military surplus gas mask. This gives you eye protection, and the built in one way flapper valves. Rig up to your garden hose (or other hose of choice) and away you go.

Breathing is labored for both of these methods. You can work under these conditions, but it isn't fun. I've done it for hours on end while basking on one of uncle sams cruise ships. But rig up a fan at the other end of the garden hose to slightly pressurize it, and breathing becomes much easier. The duct from a cars dashboard provides reasonable flow and pressure. So does a blowdrier (just turn the heat switch off). A bit of tape, and you've got a good safe forced air supply now.