Last time I checked, GPU processing has a better-bang-for-the-buck than FPGA processing, and the gap continues to widen.
In an interesting twist, The Register claims that Achronix's decision to use Intel was driven in part by national security considerations. We've reported extensively on the idea that chips fabbed overseas in insecure facilities could contain hidden kill switches or backdoors that would let an opponent cripple the US military, and Achronix allegedly wants to be able to sweeten its pitch to military customers by offering a home-grown solution.
[1] http://arstechnica.com/business/news/2010/11/intel-shifts-st...
Cool stuff, and all the more intriguing considering that Intel's getting involved.
Bang-for-buck is pretty much the name of the game in brute-force cracking. You're right that NSA probably doesn't have any budget constraints, but they'd still be interested in getting the most hashes/second possible out of $10 million.