Would be hard to just replace it with a big screen as it has to be similar in shape and size to whats there because of the boxes underneath. 
  
Could probably do a video wall of sorts, without a scale, its hard to tell how big the existing score board actually is, but could imagine you could do something, maybe slightly deeper for £20,000. 
  
Most modern solutions would come with a contract for content too, so would be an ongoing cost...