Expect to pay somewhere in the region of £120, off ebay they cost about £30 so it depends on your budget really. The quality is not bad off ebay, alot of people have bought satisfactorily off ebay.
There are various places, the stealer (the dealership) might still have them, but don't order it from them ask them to check the dealer network for one. Other places may be eurocarparts, www.gericia.com, Welcome to KMS Online but you'll have to check prices and availability.