Matthias Wandel recently did some experiments over several options. A decent furnace filter, when duct-taped to a box-fan, did surprisingly well:

https://www.youtube.com/watch?v=rDZ9yUdM2wA

It turned out that my local hardware store had a similar pre-manufactured offering with a slightly less Jerry-rigged aesthetic. We bought one for my son's allergies but I also noticed an improvement on the whole upper floor of our house. Box fans can move a lot of air. Furnace filters are cheap commodities with a large cross-sectional area that also allow a fair amount of flow.