You can get an arduino mega and ethernet shield from ebay for ~$30 shipped, so that might be a good starting point.
http://www.ebay.com/itm/1-Funduino-Mega-2560-ATmega2560-16AU-Board-Arduino-compatible-Free-USB-Cable-/251143019741?pt=LH_DefaultDomain_0&hash=item3a794a5cdd
http://www.ebay.com/itm/Ethernet-Shield-W5100-For-Arduino-2009-UNO-Mega-1280-2560-/270955738702?pt=LH_DefaultDomain_0&hash=item3f1638764e
http://www.ebay.com/itm/ATmega2560-16AU-Board-Ethernet-Shield-W5100-Arduino-2560-A067-hot-sale-/251162536643?pt=US_Radio_Comm_Antennas&hash=item3a7a742ac3