Nisbets have a decent offer on their "Vogue" diamond steel - £12 with tax, P&P included. Not quite as cheap as some of the Ebay offers from the far east, but it seems a good piece of kit at a very reasonable price.
http://www.nisbets.co.uk/vogue-diamond-sharpening-steel-30-5cm/D161/ProductDetail.raction
Martin/