Well, you can get a radial acoustic 7 array of MEMS microphones for ~$50, doing stuff with the output is the hard part. That being said, I've used one to locali

Well, you can get a radial acoustic 7 array of MEMS microphones for ~$50, doing stuff with the output is the hard part. That being said, I've used one to localisation the direction that lightning is coming from. Have no idea how good the accuracy would be, but there's likely large room for optimization in that setup; it likely just comes down to the accuracy of the microphones. I personally would go with the radar route; it's slightly more expensive that the acoustic route, but accuracy would be fantastic, even at a distance.