It's £11.99 plus £3.95 postage at Netpricedirect. Lots of other little bargains on there too.
I've used them once but it was 2 years ago however I was very pleased.
Alternatively it's available at Smyths Toys for £12.49 P&P £4.25 but perhaps you could get it in-store to save on the delivery costs? Not sure how it works as I've never used them before.