not just the nic and the antenna. youd have to get a wireless access point or wireless router then plug the extender into the connector where the regular antenna would go. there are lots of wireless routers with wired routing built right in!
if it isnt a problem you could just run teh cable to the barn/office and then waetherize teh network cable. id put it in conduit so teh cable dont get beaten by weather.
thats the easiest way to go if wireless is too expensive, just by repeater or a cheap switch and use that as a repeater.