They day I read at hackaday (http://hackaday.com/tag/esp8266/) that a new $5 wifi module was available, I order a few of them to test. Now, a few weeks later I want to share my experience.
This is a very simple demo using the ESP8266 and Arduino to update a remote server (https://thingspeak.com/) using a digital temperature sensor.
These are really exciting times for the Internet of Things (r)evolution. Prices are coming down and the Maker community is eager to develop the next generation of all things connected.
The following setup could be done under $20. This is using off the shelf "pricey" components (like Arduino), but you could program your own MCU with UART support and make it cheaper.