DIY Air Purifier

I've been having allergy problems.  A few visits to the ENT doc plus a battery of scratch tests narrowed down to a massive penicillium mold allergy.  Well, I can't get the carpet ripped out of my house for a few more weeks, but I needed something to knock down the irritant count now.  Looked at air purifiers, at the direction of the allergy specialist nurse, and talk about pricy – some up around $800.  But there's nothing exotic going on inside, no electrostatic precipitators or other tech, just a fan, a filter, and some control electronics.  So... off to the search engine of choice to look up "DIY air purifier" and here's the main result courtesy of Consumer Reports and University of Michigan.
Here's my version, front & back: 

About the only mods I made from the UofM design were to put the filter on the back of the fan, and to seal it down all around with duct tape.  It sucks down against the fan better that way, so instead of trying to blow the filter off it's being pulled into a stronger configuration and the tape job doesn't have to be as robust.  The filter is a 3M Filtrete 1900 Maximum Allergen model, about $20 at Lowe's.  Be sure to get the flow direction right when you tape it on.  There are arrows on the filter's edge and it's not hard to figure out.  The fan is an old $10 cheapie.  Luckily 20"x20" seems to be a common size for both box fans and filters, and everything meshed right up.

Cut to the chase: Yes, it works.  I haven't had a sniffle in over 48 hours now.  While I was at it, I got one for the central air system too and effectively turned the whole house into one big allergen filter.

But I still popped for a nice $130 ready-made HEPA purifier for the office.  Quieter, and with nice timer and speed controls.  It seems to work about the same otherwise.  Effective, cheap, quiet: pick any two.

Damnit, wish I'd known this two years ago.