20 BFL Bitforce Mini Rigs (each, $30k) will give about 30THash/Sec hash power for $600k. That's way above 60% of hash power of then total 51THash/Sec.
10.694M total Bitcoin * $18.5 current mtgox best ask rate = $197.839M
So, BFL should ship at least 6595 such miners, or price it based on, (total worth of all Bitcoin / no of miners planned to ship).
Does this mean, these miners priced so low, or currently bitcoins comparatively valued so high? Or, these two parameters just unrelated?
Please note that these miners are yet to be shipped.