Hi,
I read in another post that these quadratic diffusers are on special from Paul Spencer's Loudspeaker Kit company. They're reduced from $499 to $99. At that price, he'd be taking a loss, you certainly couldn't buy the materials and get them cut for a hunge. I've ordered a couple to play around with...shipping adds about 60 bucks to Sydney.
http://www.theloudspeakerkit.com/lsk-qrd-500-500-hz-quadratic-residue-diffuser-kit
I think it's an awesome deal, and even if they don't work out for me (unlikely), less than $300 is a cheap experiment in my opinion.
I just wanted to spread the word,
Phil