Replacement key fob for a Nissan Almera?

Hi, my key for remote central locking does not work. Key works in lock , starts engine etc, but it does not work remotely. Have tried changing battery, but still no joy. I have seen sites on ebay that offers to repair them for �25-30. Would it be possible/cheaper to goto a breakers yard and get the top part of a key and reprogram that for my car? thanks.