I have seasonal allergies. During the spring and fall, my allergies are terrible. I have a few air purifiers in my house, and they were not cheap. Looking for different inexpensive air purifying options, I found this video. It's a do-it-yourself air purifier using nothing more than a box fan and a furnace air filer. Check it out. 

I've never tired this. Have you tried using this purifier? Does it work?

Here's the video:

Here's another video (the guy in this video puts the filter on the back of the fan):