This sort to thing is too inexpensive to be worth tracking, it can be sent 'proof of postage' for free and if it goes missing en route you can get a full refund.
I'd expect shipping for this to be around 7 GBP depending how well you want it packaged but until it's weighed it's impossible to tell...but check here to try and figure out:
http://www.royalmail.com/price-finder