You won't get ANY sort of sound proofing that would make any difference whatsoever for £200. Look at getting some better headphones.
And I won't get any headphones that would give better reproduction than my speakers for less than a grand. I've recently spent about 100 quid total on DJ and casual headphones, I have to buy a laptop, I was looking to be considerate to my neighbours. I thought egg cartons might be a good idea, obviously not.