Fan like this:
http://www.lowes.com/pd_625625-1225-HBF2010A-WM_0__
Filter like this: http://www.walmart.com/ip/Filtrete-Advanced-Allergen-Reducti...
They even have a filter embedded with carbon if you're a smoker.
Filter like this: http://www.walmart.com/ip/Filtrete-Advanced-Allergen-Reducti...
They even have a filter embedded with carbon if you're a smoker.
Duct tape to the back of the box fan, done.