access point/ wireless router

An access point is a simpler wireless device that is primarily designed to hook up to a non-wireless router via ethernet.

A repeater/range extender may allow you to extend wireless coverage without an ethernet connection.

Another solution is to link up a second wireless router (usually via ethernet unless the devices support WDS) Used routers are common and cheap secondhand -- though you have to change certain settings before one will work as a simple access point (Netgear site has useful tips).

Probably the best solution is to dump wireless and look at homeplug type solution (mains borne network adapters).

Homeplug -- note, I don't use it, but there are lots of enthusiatstic recommendations -- uses the mains power ring in your house to communicate. It sounds scary -- but apparently it just works, is simple to set up and fast.

iwill check that out, thanks