After testing different chips/modules for WiFi, BLE beacons.

I am leaning toward to use NRF24l01+ send and listen BLE beacon frames.

The reasons:

1. TI does not provide API to use CC2540/CC2541 in sniffer mode
2. To write software on CC2540/CC2541, you need IAR, which cost $4,000 USD!
3. ESP8266 chip use too much power, it is take too long to boot and transmit the packet, the best I can do is 200ms.

Use another MCU (Arduino) with NRF24l01+ , anything can develop the firmware fairly easy. Cost will be low.