So, I did some looking around today. I was thinking about finding an old blower unit out of a forced air furnace, but no luck there. I found this little 4500 CFM swamp cooler at the local Habitat for Humanity Re-Source shop. They wanted $100 for it. I haggled them down to $75 and then got a receipt for $25 (tax deduction) for donating back the panels. Motor is in great shape and it's very quiet at high speed.

I intend to take the squirrel cage and motor out of this and make a smaller cabinet that can be put on wheels and is the perfect height for sanding. I figure I'll rig it up to take a popular size filter for air cleaning duties.
Then it occurred to me that I could also use this to help trap dust directly off the top when I'm sanding for what the dust collecter misses. Anyway, I'll have an air cleaner for my shop with another work surface...