Hi Dave, bad news I'm afraid mate they are dealer part only £214. Scrappers will only sell you the complete hub thing with the sensor. The sensors rust in and are a bugger to get out, certainly can't without breaking them. If your's has gone like mine it is the wires that have broken. It's usually the NSF, don't know why. Mine had been repaired before and not sealed so the water had bled through the wire corroding the lot, I managed to hack saw part of the case off to find good wire to solder. If you trace the wires from the sensor it clamps to the suspension arm and has thicker insulation just there and that is where it normally breaks. If your lucky you will be able to rejoin the wires there, if not trace the wires back until you get clean copper to solder and replace all the way up to the plug in the engine bay. Once you have repaired it make sure the cables are well sealed from the water.
Let me know if you need any more advice.
Jim