Easiest method is to use zoning. For each zone you need a microphone, op-amp and analogue channel. The analogue part will be the most annoying part. an analogue multiplexer IC will do the job nicely though.
Just cycle through the analogue pins and take a rolling average of each pin's (Root Mean Squared) value. This should approximate the volume on each mic. So long as you partially shield the microphones, it should be quite directional.
If you use maybe 16 microphones, that needs:
1x Arduino
2x 8 way analogue multiplexer IC
4x quad op-amp IC
various resistors for balancing op-amps etc.
Enough to look impressive in a breadboard, but not too hard, or expensive to build.