BFL ASICs ROI gets shaky with a $60 bitcoin at 1,500,000,000 difficulty ... but I guess there's Europeans with 50c per kilowatt/hour power bills.
I think you added a few too many zeros.
http://www.coinish.com/calc/#BFL 50GH/s @ $2499 (straight from their product page) will never generate a return @ 80,000,000 difficulty, $94/BTC and 1.2788% growth rate.
ASICMiner is looking at this same curve. Very soon it will not make sense for ASICMiner to deploy their own hardware.
The BOM on the USBs is ~$4. Of course it will be.