I would buy the ones you've seen on ebay. That price is about right and they are off a Ford dealer so won't be wrong.

The sensors come on the pads. They tell you when your pads are low.

P.s. If you want to save yourself some money, buy some Apex or Mintex discs and pads. They are half the price and equally as good.

Im a mechanic and see no point in these super expensive parts. They meets the Eu standards, as do the cheaper brands and do exactly the same thing.