I was looking to buy a 200m reel of string, probably ashaway or yonex.
Something durable, bg 65 or ashaway rally.
I was wondering if anyone knew of some good deals on 200m reels.

The best I could find are these:
http://gefensports.co.uk/sqbastrings.html
http://www.watdon.co.uk/wd-strings/
http://www.stringsnthings.org.uk/mainsite.html

Any recommendations / pointers?

Have you tried the following:
http://www.rapidrepair.biz/rr-shop/home.php

I hear only good things about Watdon too. You may want to call them to see what exactly they have for sale as I hear not all is shown on their website.