um .. what?
Are you talking about having the right wireless frequency/standard?
Why would they need to buy anything but the router? are cables out of the question? I don't get this response, and I think you are wrong.
DON'T BUY ANYTHING EXTRA!
Since you already have the PC, and you are replacing an existing router, you have all the stuff you need. just buy the new one, and replace. simple, easy, and cheap.