Here we go again in the USA new economy.... I checked online at Home Depot for the 20" box fan,,,,they had stock at my local store, just not out for display due to seasonal sales. Setup pickup at my local store and bamb...$16.01 and it was mine. I then stopped by furnance filters and snagged a couple 20" square filters for $1.88 each. Got it setup with a thicker type double faced tape and bingo off to the races.
I just position the fan to "suck" dust at each machine I use at the time... works GREAT and I can vac off the filter as I go also.
Sure am glad I have my shop in my basement.... usage year round, can control humidity, and now my dust is under control within my new economy budget.