Unless you want to spend $5-10M in NRE, you're going with a structured ASIC process. eASIC and Alterra HardCopy are the only options here. Chips will be capable of 2GHash/s each, approximately. So, assuming BFL is using a structured ASIC process to keep NRE less than millions, they'd need 500 ASICs to generate a terahash. Unit costs are small if you produce 10,000s of ASICs; however, when your production is in the hundreds or low thousands, you're looking at $100s per unit. That terahash box has a cost base of $500K, by our estimation.
I would love to know if you have actually seriously investigated a full custom or standard cell ASIC and have actually got quotes to justify the $5-10M NRE that you mention. Is that a figure you actually priced out? Since it's apparent you won't be going that route, I'm sure there's a bunch of people here who would love to hear the quotes you've gotten for different nodes for things like the mask set, packaging, test wafers, per wafer prices, etc.