[dharma1]

I hope a chinese manufacturer makes one soon. The teardown for Echo had the parts for a bit more than that, but you could do it cheaper, multichannel ADC and half a dozen MEMS mics. I guess drivers would be the time consuming bit

[alexforencich]

The board actually doesn't appear to have an ADC, the microphones output pulse density encoded digital data wich can be directly received and interpreted by the processor.