The ESP8266 is a WiFi SoC. The Huzzah ESP8266 breakout costs $9.95 (qty 1) when purchased from Adafruit. It is a FCC approved ESP8266 module and has a metal cover to reduce RF emissions.
Serial pass through program - version for mbed LPC1768 pins 28,27 9600 baud
See https://developer.mbed.org/teams/Ece-4180-team-who/wiki/Using-Adafruit-ESP8266-Huzzah for complete setup details and a web page server example. An external 5V power supply is needed. The library code is under development, but the web page server example does not use it.