OK, will try the dealer then. I just assumed that they'd have the usual Ford 10000% mark-up (especially after discovering that they want £18 for the little metal heat shield that goes on the lower ball joint )...
Got a used one from eBay for £12 incl. delivery. New (genuine) ones also available from Ford dealers on eBay for £17.50.
Not sure about the eBay sellers who are selling used ones for £19.99. And one that is selling a used, and obviously quite dirty, one for £25 + £9 postage - what are they thinking?