I am just slapping things together our of curiousity but this McMaster-Carr although it looks ugly/odd will get you down to 0.3microns without breaking the bank.
I guess my core question is, why does it take thousands of dollars to do? I understand if you are buying idiot proof tested products which can do it. Even then thousands seems a bit much. What part is costing so much? Fans and filters are cheap.