This whole testing fiasco is really a wonderment. To lose that many precious (and expensive) chips to only gain a marginal amount of useful information is insane. At any company I have worked for that kind of decision would have landed someone a pink slip.
To be fair, the cost of a processed 65nm wafer is likely somewhere between $1500-$2000. Not exactly a fortune.
Avalon pays (it is estimated) about 4k per wafer at 110nm.
How is BFL paying half that at 65nm? Somehow your estimates sounds kinda off.
Actually my estimate is if anything, rather high for a 200mm wafer. Have a look here:
http://www.gsaglobal.org/email/2010/general/0222w.htmIf they are using 300mm wafers it might be over $2000, but it still wont cost a fortune, particularly not on such old processes. Note that this doesnt include testing, dicing and packaging, which may cost more than the wafer, but BFL didnt do that on their "burnt" wafer anyway.