If you find the wireless version too expensive, then this ehternet lan version is the good alternative. Affordable but will enable your arduino pro mini based device to connect to an existing local area network.

• New design with Best quality.
• Mini version, more convenient to use

1. Chip board ENC28J60/SS.
2. The board 25MHZ crystal.
3. The network interface board HR911105A.
4. 3.3V power supply pin.
5. Size: 48.8 (mm) x 18.5 (mm).

the web app that is used to turn on/off the light is hosted by the arduino uno.

Here's the simple tutorial on how to use this device:

http://blog.roman-mueller.ch/index.php/2012/10/03/connecting-the-enc28j60-ethernet-breakout-board/