so, those chips are $152 each
Yeah, roughly, depending on the exact model and quantity. Don't forget the cost of the board though.
what is the board to put a shitload of them on?
You'll need to build one. Design and order a 4layer PCB containing the neccessary voltage regulators, clock generation and means of communication (JTAG, and maybe I²C, RS232 or USB?).
Has anyone tried this with more than one fpga chip? does it scale fully?
There are already some people running multi-FPGA mining setups. And yes, it does scale fully (~190MH/s per chip, can possibly be optimized even further), and if you also account for the PCB manufacturing and assembly costs, even more than that.