Cheapest WiFi Module

[NZ0I]

So far, this is the cheapest practical solution I've found for adding WiFi to transmitters and receivers: https://www.adafruit.com/product/2471.

[NZ0I]

Wait, there's a new low-price winner: WEMOS D1 Mini Lite. At US$ 3.00 plus US$ 1.76 shipping, it comes to a whopping $4.76. There is a long lead time for orders however.

There seems to be a lot of activity with these tiny IoT devices that use the ESP8266. There is even a free on-line custom build server for building firmware to run on these devices. This brief tutorial covers all the basics of using them. Quite amazing.