WOW! That's awesome and it looks relatively inexpensive to make. I really like it. I can tell you definitely have some ingenuity!
What did you end up using for the HEPA filter and where did you get it?
Well, the HEPA filter I bought from Menard's. I don't know if you have them where you are but it's similar to Lowe's or Home Depot. The brand is HEPAtech and its a replacement for an air purifier. It says it catches particles 99.97% effectively @ 0.1 microns. Cost $20-$25! I thought most HEPA filters were expensive and where rated @ 0.3 microns?
And the cost wasn't bad, pretty sure it was well under $200. The blower was the most, the rest is heating/AC supplies and sheet metal, under $70 for that stuff.