Is it against the rules to argue against BIFL? I can't find one of these for less than $250, BIFL units are $1000.

We get great performance from a 20x20 MERV 13 filter, fashioned to fit over a 20-inch box fan from Walmart. Decorative duct tape can hold it on and you're good for a year or two. I DIY-ed plastic clips out of thermoplastic, screwed to the fan body. It's lasted 4 seasons now. MERV-13 filters are $15, fans are $20, I can buy 10 complete homebrew units out of my local discount store for $350.