http://www.broadbandcarrier.net/
Have a look at this you already have the wiring in your house, all you need is adapters that plug into mains sockets
This is first google i found not cheap but so easy ,you can take you network socket anywhere around the house and I would imagine through an extension lead into garden etc
http://www.broadbandstuff.co.uk/prod...e58809a210d271
cheaper
http://www.shopmagenta.com/product/spleth.aspx?advert=4
cheapest