Just thought I'd pop a quick note up to describe a project I've just finished working on in case it is of interest to others. The project is basically a set of WiFi-enabled temperature sensors that I built from relatively cheap components, that I am now using to monitor the temperature of all of the refrigeration equipment at the Baw Baw Food Hub on an hourly basis. This will allow us to pick up any issues with the equipment in real-time, which is important as we usually only visit the hub two or three days a week.
The sensor is built around an ESP8266 wifi module, which is tiny chip that is able to be programmed as a standalone component using the Arduino IDE. The version of the chip that I used is made by Adafruit and includes a breakout board for connecting all of the things to.
The other major component I used is a DS18B20 digital temperature sensor. I bought this version that comes pre-wrapped in a waterproof sheath. I experimented with an analog sensor (TMP36) but I found the readings to be pretty inaccurate (often out by a couple of degrees C).
Other than that, all you need is a battery pack (5-6V, I used 4xAAs) some wire and a tiny breadboard to stick it all into and you have your wireless temperature sensor! You can buy all of these components from Australian-based electronics suppliers for around $30-$40. I bought from Little Bird Electronics, but they were pretty slow (didn't seem to actually have anything in stock), so I would probably suggest going with a different supplier...(https://tronixlabs.com.au/ looks good?)
The project also depends on having a web-server set up to receive HTTP requests made by the chip. I built an API endpoint from scratch for this purpose, but I have noticed that there are a lot of cloud-based services set up for exactly this use case (http://dweet.io/ for example), for those who aren't interested in building a custom solution.
I am happy to share my full component list, wiring and the code I used to program the chip if anyone is interested.