It's called the FPGA/ASIC clusters already owned by big financial players/knowledge management/intelligence communities.
Do you even know what "ASIC" stands for?! Probably not, or you would know, why what you just said is completely stupid.
About FPGAs: They are maybe good at MH/W performance, performance per chip wise they quite honestly seem to suck though.
FPGAs are not exactly cheap, but they're quite powerful.
An XC6SLX150 will get you ~200MH/s for ~20W. And if you build an FPGA cluster yourself, you'll end up with costs around 200-300$ per chip. Because they don't use much power you can reach very high density. Oh, and ASICs might actually be feasible once you reach quantities >10000.