What is interesting is, that when I shopped around, I found quite a lot of FPGA PCI board that although dang expensive, had ridiculous computing power and pretty heavy amounts of RAM. Some of them used for development or medical imaging.
The only thing they've got going for them is that they're hyper efficient, with the same hashing as a high-end GPU, but at a fraction of the energy usage, and they're a lot more expensive. They're only worth it if you were planning on running them dozens at a time, if they were as cheap as a regular GPU people would be jumping on them.