When we looked at WiFi modules, the cheapest were <$2.00 those were chip antenna based. The module we eventually settled on was still < $10 but allows an external antenna. Software extensions allow microsecond level synchronization between speakers. Latency is is sufficient for almost all applications and getting better. Acceptance is slow but growing. Live music applications will be slower to accept, the risk is high, but control functions will be the leading edge, then wired, then wireless where failure costs are contained. Leveraging mass adoption technology while maintaining private networks is hard to beat for cost, features and reliability.
My experience with microphones is it is all proprietary, low latency, was mostly analog if I am not mistaken. That price likely includes the microphone too?
Wireless transmitter/receivers have existed for speakers at <$1000/pair for a long time. All proprietary / low latency. Probably not audiophile quality.