Microsoft has released a new Surface accessory to allow access to a network through a standard RJ-45 cable when Wi-Fi is not available. During my trip to MMS 2013 in early April, this would have come in handy, however I did source a 3rdparty component that does the same thing and for much less than the Microsoft Store's $39.99 price tag.
You can find the new Surface accessory release by Microsoft here: Surface USB to Ethernet adapter
Microsoft indicates on the Store page that the device was designed exclusively for Surface with Windows 8 Pro.
If you're interested in a less costly device that I know works well, check out the one from Plugable Technologies instead:
The Plugable version is just $13.95 from Amazon.com and if you're a Prime member (and, who isn't?) the device will show up in a couple days without any additional shipping costs.